Molokai Sweet Potato Mille-­Feuille from Thomas Keller's cookbook "The French Laundry, Per Se."

If you’re looking to level up your home cooking, consider Thomas Keller’s new cookbook a masterclass. “The French Laundry, Per Se” is the chef’s first cookbook release in more than a decade, and captures the link and collaboration between the chef’s two restaurants — one in California, the other in New York. The book includes 70 recipes, and although not the most accessible guide (this is French-style fine-dining cuisine, after all) there are plenty of techniques for beginner cooks to take in and learn from. Readers will find recipes for dishes like Frost-kissed Garden Cauliflower, Charcoal-Grilled Japanese Eel –— and even noncooks will find artful plating to admire and a selection of essays from chefs at the restaurants.

Below, a recipe excerpt from the book.

Excerpted from The French Laundry, Per Se by Thomas Keller (Artisan Books). Copyright © 2020.

Molokai Sweet Potato Mille-­Feuille
Compressed Asian Pear, Chrysanthemum Shoots, and Caramelized Onion Jus

Makes 6 servings

175 grams clarified butter (page 53)
400 grams peeled Molokai sweet potato, about 2½ inches (6.5 centimeters) in diameter
200 grams peeled russet potato, about 2½ inches (6.5 centimeters) in diameter
8 grams kosher salt

Compressed Asian Pear
90 grams water
90 grams sugar
30 grams yuzu juice
Sea salt
1 Asian pear

Caramelized Onion Jus
100 grams sherry vinegar, plus more to taste
875 grams water
600 grams sweet onion essence (page 288)
600 grams mushroom essence (page 289)
15 grams dehydrated caramelized onions (recipe follows)
7 grams thyme sprigs
3 garlic cloves, skin on, smashed
1 bay leaf
12 grams Pre-­Hy (page 109)
Kosher salt

Creamed Arrowleaf Spinach
75 grams whole butter
100 grams diced leek (white and light green portions only), rinsed to remove any dirt
200 grams heavy cream
500 grams stemmed arrowleaf spinach leaves
8 grams Pre-­Hy
Kosher salt

To Complete
40 grams potato flakes
1 recipe cornstarch–egg white paste (page 235)
30 grams clarified butter, or more as needed
Chrysanthemum shoots

Special Equipment
Chamber vacuum sealer (optional)
Japanese mandoline
Immersion circulator (optional)
Flower-­shaped cutter, just over ½ inch (13 millimeters) in diameter
Combi oven (optional)

This dish originated because of the shape of the vegetables we were using. We’ve always done some form of mille-­feuille potato, a shingled or scalloped dish. When we found ourselves with a colorful variety of small marble potatoes, we scalloped them in a sheet pan, making a virtue of their varying sizes and colors. When we discovered the richly flavored purple Molokai sweet potato, we used this same technique. We love its deep coloring, its sweetness, and the savory depth of the spinach, pear, and onion jus that makes this vegetarian dish as satisfying as a meat course.

SEE ALSO: NYC Chefs Launch Cookbook to Benefit Restaurant Relief Fund

For the Mille-­Feuille
If you have a chamber vacuum sealer, put an eighth sheet pan in a 12-by-15-­inch (30-by-40-centimeter) sous vide bag, place in the sealer chamber, and vacuum seal. If you do not have a chamber vacuum sealer, spray an eighth sheet pan with nonstick spray. Line the pan with two layers of plastic wrap, extending it over the sides.

Put the clarified butter in a wide 3-­quart (3-­liter) saucepot, heat just enough to melt the butter, and keep warm.

Set a Japanese mandoline over a bowl. Slice the potatoes lengthwise into 1-­millimeter-­thick (paper-­thin) slices. Adjust the blade as necessary to be certain that the slices are solid and of even thickness. Season with the salt. Gently toss the potato slices in the pan with the clarified butter to coat.

Overlap (shingle) the potato slices, alternating between the sweet potatoes and the russet potatoes (use 2 slices of sweet potato, then 1 slice of russet), in even rows to cover the bottom of the prepared sheet pan in a solid layer. Cover the potatoes with a piece of parchment paper, set a second eighth sheet pan on top, and press down to secure the potato slices in place.

Remove the top pan and the parchment and arrange a second layer of potato slices over the first. Continue to layer the potatoes, pressing with the parchment and sheet pan after each layer is complete. The final layer of potatoes should be level with the rim of the pan.

If you have a chamber vacuum sealer, set an immersion circulator in a water bath and heat the water to 88°C (190.4°F). Wrap the entire sheet pan twice in plastic wrap, place it in a 12- by 15-­inch (30- by 40-­centimeter) sous vide bag, and vacuum seal. Cook in the water bath for 1½ hours. Remove from the water bath and let rest for 15 minutes, then submerge in an ice-­water bath until cold. Refrigerate for up to 2 days.

If you do not have a chamber vacuum sealer, preheat the oven to 300°F (150°C). Place a piece of parchment on top of the mille-­feuille and seal the pan with a piece of aluminum foil. Bake for about 1 hour, until a cake tester inserted into the potatoes meets no resistance. Remove the foil but leave the parchment over the top. Set a second eighth sheet pan on the parchment and add weight to the pan to compress the potatoes; let stand for about 30 minutes. Transfer the potatoes with the weights to the refrigerator and refrigerate for at least 6 hours or up to 2 days.

For the Compressed Asian Pear
Combine the water, sugar, and yuzu juice in a 2-­quart (2-­liter) saucepot and warm over medium-­high heat, stirring often, just enough to dissolve the sugar. Pour the syrup into a bowl and season to taste with sea salt. Nestle the bowl in an ice-­water bath and let cool completely.

Peel the pear and slice it just under ¼ inch (6 millimeters) thick on a Japanese mandoline. If you have a chamber vacuum sealer, put the slices of pear and the syrup in a sous vide bag. Place in the sealer chamber and vacuum seal. The pears can be used immediately or refrigerated for up to 3 days. Punch it with a flower-­shaped cutter just over ½ inch (13 millimeters) in diameter just before using.

If you do not have a chamber vacuum sealer, punch the pear with a flower-­shaped cutter just over ½ inch (13 millimeters) in diameter and place the pieces directly in the syrup. Refrigerate in a covered container for at least 24 hours or up to 3 days.

For the Caramelized Onion Jus
Reduce the vinegar in a 4-­quart (4-­liter) saucepot over high heat until the pan is almost dry.

Add the water, onion essence, mushroom essence, dehydrated caramelized onions, thyme, garlic, and bay leaf to the saucepot. Bring to a boil, then reduce the heat and simmer for about 15 minutes.

Place a dampened tea towel in a strainer set over a medium bowl. Strain the liquid into a 2-­quart (2-­liter) saucepot. Bring to a simmer and reduce to 300 grams.

Strain the liquid into a blender. With the blender running on medium speed, add the Pre-­Hy and blend to combine. Season with additional vinegar and salt to taste. Strain through a chinois into a container and cover.

Refrigerate for up to 3 days.

For the Creamed Arrowleaf Spinach
Heat the butter in a 1-quart (1-liter) saucepot over medium-­high heat until it begins to brown.
Add the leek to the saucepot and sweat over low heat until tender, about 30 minutes.

Add the cream to the saucepot and bring it to a boil. Cook, stirring often, until the cream mixture is very thick. It will have the consistency of a glaze and look as though it is about to split.

Bring a pot of water to a boil. Blanch the spinach in the boiling water until tender, about 3 minutes. Drain the spinach and transfer to a clean kitchen towel. Wring out any excess moisture. Place 135 grams of the spinach in the blender. Add the glazed leek and Pre-­Hy; blend until smooth, using the tamper to help the mixture combine. Taste the creamed spinach and season with salt. Keep in a warm spot for up to 4 hours before serving or transfer to an airtight container and refrigerate for up to 2 days.

To Complete
Warm the caramelized onion jus and the creamed spinach in separate saucepots, if needed. Fill a disposable piping bag with the creamed spinach and pipe it into a small squeeze bottle.

Remove the mille-­feuille from the refrigerator and work with the potatoes while they are cold.

Remove the weights or plastic. Lift the potatoes from the pan and place on a cutting board.

Trim just enough of the mille-­feuille to smooth the edges. Cut crosswise in half, then cut each half crosswise into 3 equal portions.

Lightly crush the potato flakes in your hands and place in a shallow bowl. Put the cornstarch paste in a separate shallow bowl. Dip the bottom of each mille-­feuille in the cornstarch paste, then dip in the potato flakes to coat.

Heat the clarified butter in a large sauté pan over medium heat. Working in batches, add the mille-­feuille to the pan, crust-­side down, and sauté for 2 to 3 minutes, until the bottom is golden brown. Transfer the mille-­feuille to a cutting board, crust-­side down, and cut each piece into 3 equal pieces. Drain briefly on paper towels. Repeat with the remaining mille-­feuille. If the mille-­feuille have cooled before you’re ready to serve them, transfer them to a rack set over a sheet pan and rewarm in a preheated 375°F (190°C) oven for about 6 minutes, until warmed throughout.

Arrange the mille-­feuille on the serving plates. Garnish with pieces of the Asian pear, dots of the creamed spinach, and chrysanthemum shoots. Spoon a few pools of the caramelized onion jus onto each plate.

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Dehydrated Caramelized Onions

Makes 60 grams

700 grams yellow onions
10 grams canola oil
500 grams water

Special Equipment
Japanese mandoline

Cut ¼ inch (6 millimeters) from the root end and ½ inch (1.25 centimeters) from the stem end of the onions. Halve them through the root and peel them. Using a Japanese mandoline, slice the onions lengthwise into pieces as long and thin as possible.

Spread the onions in a shallow layer in a wide saucepot. Add the oil and cook over medium-­low heat, stirring often, for 8 to 10 minutes, until the natural sugars in the onions caramelize to a rich golden brown without burning.

Once a layer of caramelization or fond has formed on the bottom of the pan, add one-­third of the water and use a silicone spatula to deglaze the pan. Cook until the pan is dry. If the pan begins to scorch, transfer the onions to a clean pan. Cook until the onions are a very dark brown, about 1 hour 20 minutes total, deglazing twice more when the fond builds up on the bottom of the pan.

Line a sheet pan with a nonstick silicone baking mat and spread the onions in a 9 by 12-­inch (23 by 30-­centimeter) layer over the mat. Dry in a dehydrator set to 150°F (65.5°C) for 14 to 18 hours, until the onions are very dry. The onions must be crisp when cool.

Use the dehydrated caramelized onions as is, or grind into a powder in a spice grinder to use as a seasoning. Store in an airtight container at room temperature for up to 3 months.

Clarified Butter

Makes about 280 grams

450 grams whole butter, cubed

Traditional method: Place the butter in a 1-quart (1-liter) saucepot and melt over low heat, without stirring. Once the butter has melted, it will separate into three layers. Skim off and discard the foamy layer of milk solids floating on top. The clear yellow butter beneath it is the clarified butter. Carefully pour it into a container, leaving the milky liquid at the bottom behind. Use immediately, or cover and refrigerate for up to 10 days or freeze for longer storage.

Refrigerator method: Bring a stockpot of water to a simmer. Place the butter cubes in a heavy-duty resealable kitchen bag and seal. Set the bag in the simmering water to melt the butter. Transfer the bag to an ice-water bath, positioning the bag at an angle with one bottom corner of the bag in the most downward position. Refrigerate until the butter has solidified.

Remove the bag from the refrigerator, hold it over a bowl, and snip the bottom corner to allow the liquid to drain into the bowl. What remains is a solid block of clarified butter. Rinse it under cool running water for a few seconds to remove any remaining milk solids, then dry. Store, well wrapped, in the refrigerator for up to 10 days or freeze for longer storage.

Sweet Onion Essence

Makes about 600 grams

2,000 grams peeled yellow onions
250 grams water
40 grams peeled garlic cloves
5 grams thyme sprigs
3 small bay leaves

Special Equipment
Meat grinder with a medium die
Pressure cooker

In the restaurants, we make large quantities of onion essence, so we strain the stock through a tea towel-lined perforated hotel pan. We top the onions with another hotel pan and weight it, then let it stand for 30 minutes to extract as much essence as possible. The best way to get flavor is through single ingredients, but here we’re adding a few aromatics. Reduced down, this essence is almost like a demi-glace — it’s so full and sweet. You can add kombu for more body and a meaty umami flavor. This, too, is used in braising and glazing and sauce making. As with all essences, this can be thickened with a liaison to make its own sauce.

Cut the onions in half through the root end. Trim off the root end and stem end and discard. Cut the onions into pieces that will fit into the meat grinder. Grind through the medium die into a bowl.

Place the water, garlic, thyme, bay leaves, and onions in a pressure cooker. Cook on high pressure on the 10-minute setting according to the manufacturer’s instructions, then carefully release the pressure.

Line a fine-mesh strainer with a tea towel and set it over a medium bowl. Strain the stock through the tea towel and let cool, then wring the tea towel to extract all the stock from the onions. Discard the solids in the towel.

Store the stock in an airtight container in the refrigerator for up to 3 days or freeze for 3 months.

Mushroom Essence

Makes 600 grams

750 grams button mushrooms
150 grams water

Special Equipment
Meat grinder with a fine die

This is the veal stock of the vegetable world. Like most essences, it’s been streamlined. Have a look at the mushroom stock in The French Laundry Cookbook — there are many ingredients and hours of cooking and reduction on the stove. Here, we use nothing but mushrooms, ground, and just a small amount of water to get them weeping. We squeeze them aggressively to get all the liquid we can out of them. And the solids are still pretty tasty and make a great vegetarian meat loaf or stroganoff for a satisfying vegetarian staff meal.

Wash and dry the mushrooms. Grind them through the fine die of a meat grinder. Place the mushrooms and water in a 4-quart (4-liter) saucepot and bring to a boil over medium heat.

Reduce the heat to maintain a simmer and cook, stirring from time to time, for about 5 minutes, until the mushrooms are cooked. Cover the saucepot with a lid and steep for about 30 minutes.

Line a fine-mesh strainer with a tea towel and set over a medium bowl. Pour the mushroom mixture into the strainer and allow the mushrooms to sit for about 1 hour to drain thoroughly.

Lift, twist, and squeeze the tea towel to drain any remaining essence from the mushrooms; discard the mushrooms. Store the essence in an airtight container in the refrigerator for up to 3 days.

Pre-Hy (Prehydrated Xanthan Gum)

We’d like to call special attention to one liaison that we find profoundly useful when it’s properly diluted: xanthan gum. Xanthan gum is one of the most often used and versatile liaisons, but it is severely potent. Just a little bit can achieve dramatic results. Add too much, however, and it’s time to “begin again,” as David says. It’s so powerful in powdered form that it’s easily mismeasured. If you’re off by a tenth of a gram, you can ruin a whole sauce. To solve this problem, David developed what we call prehydrated xanthan gum, or Pre-Hy, as it’s known in both kitchens, in effect diluting the powdered xanthan gum and making it much easier to use, a real game changer for us.

1%: Emulsification
2% All-purpose Pre-Hy
3%: Bouillon consistency
5%: Velouté consistency
15%: Fruit or vegetable glaze (with 1% Ultra-Tex)

To make our all-purpose Pre-Hy, which is used throughout the book, put 1,000 grams of water into a blender. With the blender running on low speed, shear in 20 grams of xanthan gum while slowly increasing the speed to high. The xanthan gum should completely hydrate in the water. If you have a chamber vacuum sealer, pass the mixture through a chinois into a container and place the container, uncovered, in the sealer chamber. Run a complete cycle on full pressure to remove any air bubbles incorporated during blending. It will produce a clear gel, which will contribute to the clarity of the sauce or puree it will eventually be used in.

Pre-Hy is cold-soluble, so it can be mixed directly into liquid in a Vita-Prep (or Vitamix) to add viscosity. At 1%, the Pre-Hy is the perfect aid in a powerfully bound mayonnaise and a useful stabilizer of simple emulsified oil-and-vinegar-based vinaigrettes. At 3%, it adds just a hint of body to an otherwise thin juice or broth. That’s all it needs to hang on the palate a little longer and therefore add to the perception of depth of flavor and satiety. When 3% is added to a beurre blanc or beurre monté, it becomes a stable butter glaze resembling a beurre fondue. At 5%, added to our classic creamy lobster broth or other creamy broths, it keeps the cream and stock perfectly emulsified and holds the frothy bubbles that we like so much. And finally, at the highest concentration, 15%, in tandem with a small amount of Ultra-Tex, marinades or poaching liquids can be thickened to coat fruits and vegetables in a shiny glaze.

Cornstarch–Egg White Paste

Makes 170 grams

100 grams egg whites
70 grams cornstarch

Whisk the egg whites and cornstarch together in a small bowl until thoroughly combined. If not using immediately, whisk the paste again just before using.

"The French Laundry, Per Se" by Thomas Keller.

“The French Laundry, Per Se” by Thomas Keller.  Courtesy

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