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PAN-ROASTED MUSHROOM & KALE SLAB PIE

SERVES 12-15

I learned to pan-roast mushrooms while watching Chef Patrick O’Connell at his emerald green cooker at the Inn at Little Washington. Sauté them in a pan that’s as hot as possible in hot, hot oil. Be bold and don’t touch them until they release from the pan readily and are deeply bronzed, not wrinkled or desiccated, then do the same on their other side. What emerges are sturdy, meaty mushrooms, a key ingredient in this pie, with their woodsy flavor and substantial texture. This is a slim, quiche-like slab full of flavor and texture, the kale’s vegetal addition balancing the filling’s rich, onion-studded custard. Cut this pie into small pieces as a pass-around appetizer, or serve larger pieces—with a salad—for Sunday brunch, weekday lunch, or light supper fare.

Make Ahead: Pan-roast the mushrooms a day ahead. This pie reheats very well.

ALL-BUTTER CRUST

  • 2-1/2 cups plus
  • 2 tablespoons (325 g) all-purpose flour
  • 16 tablespoons (225 g) unsalted butter, cubed and frozen for 20 minutes
  • 1/4 teaspoon kosher salt
  • 1/2 cup (120 ml) ice water

FILLING

  • 1/4 cup (60 ml) olive oil
  • 6 ounces (170 g) shiitake mushrooms, stemmed and thickly sliced (about 3/2 cups)
  • 1/4 teaspoon kosher salt
  • 1/4 teaspoon red pepper flakes
  • 6 ounces (170 g) cremini mushrooms, stemmed and sliced (about 3-1/2 cups)
  • 2 tablespoons dry sherry, optional
  • 2 medium onions (285 g), sliced in 1/4-inch-thick half-moons
  • 1 teaspoon fresh thyme leaves
  • 3 cups (426 g) frozen chopped kale, thawed and squeezed dry; or
  • 5 cups (426 g) finely chopped stemmed fresh kale
  • 1 cup (240 ml) whole milk
  • 2 large eggs plus 1 egg white
  • 3/4 teaspoon kosher salt
  • 1/2 teaspoon freshly ground pepper
  • 4 ounces (113 g) Gruyère cheese, grated (about 1 cup)
  • 1 egg yolk
  • 1 teaspoon water
  • 1/4 teaspoon kosher salt

DIRECTIONS

For the crustIn the food processor, pulse the flour, butter, and salt until the butter is in small pieces coated with flour, about 15 times. Add the water all at once and process until the mixture almost forms a ball. Form the dough into a 6- by 4-inch rectangle using plastic wrap and a bench scraper to firmly press the dough into a cohesive form. Wrap tightly and refrigerate a minimum of 4 hours.

Remove the dough from the refrigerator and allow it to warm slightly. Divide the dough into two pieces, one slightly larger than the other. Roll out the larger piece to 11 by 15 inches and place in the slab pie pan, pressing it into the corners of the pan and allowing the excess to drape over the sides. Refrigerate. Roll out the second piece of dough to 10 by 14 inches, place it on a lightly floured sheet of parchment, and refrigerate.

For the fillingPour 1-1/2 tablespoons of the olive oil into a wide skillet and set over high heat until the oil shimmers. Add the shiitake mushrooms and push them around into a single layer. Sprinkle with half the salt and red pepper flakes and leave the pan alone until one mushroom, tested, can be lifted easily without sticking, a good 6 to 9 minutes. Be brave: The mushrooms will smoke, snap, and sizzle. Turn all the mushrooms quickly and cook until the other side is equally browned, another couple of minutes. Transfer the shiitakes to a bowl. Repeat the pan-roasting process with another 1-1/2 tablespoons oil, the cremini mushrooms, and salt and red pepper. Return the shiitakes to the pan. If using sherry, add to the pan and cook over high heat until the scent of alcohol has diminished and most of the liquid has evaporated. Remove the mushrooms to a bowl.

To the pan, add the remaining 1 tablespoon olive oil. Reduce the heat to medium-high and add the onions and thyme, stirring to coat with warm oil. Reduce the heat to medium and cook gently until the onions are soft and golden brown, about 15 minutes. Stir in the kale and remove from the heat.

Heat the oven to 400°F; if you have one, place a baking stone, Baking Steel, or inverted baking sheet on the center rack to heat.

Scatter the mushrooms along the bottom crust, add the kale and onions, and gently push the filling around and into the corners of the crust.

Whisk the milk, eggs, and egg white together with the salt and pepper. Pour the eggs over the filling and distribute the grated cheese across the whole beautiful thing. Drape the top crust across the pan. Crimp and slash. Whisk the egg yolk and water in a small bowl. Use a pastry brush to paint the top of the crust. Sprinkle with salt. Chill for 20 minutes, if you have time. Otherwise, slide it into the oven (on top of the steel, stone, or baking sheet if using) and bake until a knife inserted into the pie comes out clean, 45 to 50 minutes.

Cool for at least 10 minutes before portioning. Refrigerate leftovers and bring them back to room temperature to serve, or wrap in foil and reheat at 350°F for 15 to 20 minutes.