Rich and meaty, duxelles is a mixture of finely chopped mushrooms, shallots, and herbs, simmered in butter and reduced until thick and fragrant. Here it is rolled in a nut-studded pastry. These crispy savory rounds should be baked in advance and served at room temperature.
2 c. all-purpose flour
¾ c. (1 ½ sticks) cold unsalted butter, cut into 1-inch pieces
¼ c. coarsely chopped walnuts or pecans, ground
½ tsp. salt
1 tsp. fresh lemon juice
1 tbsp. ice water, or as needed
3 tbsp. unsalted butter, divided
¼ c. minced shallots
2 cloves garlic, minced
5 ounces cremini or white mushrooms, finely chopped (3 cups)
3 ½ ounces fresh shiitake mushrooms, stemmed and finely chopped (1 cup)
1 tsp. fresh thyme, or ¼ tsp. dried
2 tsp. minced fresh chives
1/8 tsp. salt
To make the pastry: Combine the flour, butter, nuts, and salt in a food processor; process, using a pulsing motion, until the mixture is crumbly. Add the egg and lemon juice; continue pulsing until the mixture begins to stick together. While the blade is spinning, add the water, 1 tablespoon at a time, just until the mixture forms a ball.
Divide the pastry into 2 balls; wrap in plastic wrap or seal in plastic bags. Refrigerate for at least 1 hour or overnight.
Meanwhile, to make the duxelles: Melt 1 tablespoon of the butter in a large nonstick skillet over medium-high heat. Add the shallots and garlic; cook, stirring constantly, until the shallots are translucent, about 2 minutes. Melt the remaining 2 tablespoons butter in the pan; add the mushrooms and thyme. Reduce the heat to medium. Cook, stirring occasionally, until the liquid is completely evaporated and the mushrooms are tender, 8 to 10 minutes. Stir in the chives and salt. Taste and adjust the seasoning. Let cool.
To make the pinwheels: Preheat the oven to 375° F. Line a baking sheet with parchment paper. Place 1 ball of dough on a work surface covered with a sheet of waxed paper. Top with another sheet of waxed paper and press with the palm of your hand to flatten the ball. With a long side toward you, roll into an 8-by-10-inch rectangle. Repeat with the remaining pastry.
Remove the waxed paper from one pastry sheet. Trim to even the edges. Spoon half of the mushroom mixture onto the center of the pastry; use a rubber spatula to spread it in an even and thin layer to the edges. Use both hands to lift the long edge of the pastry nearest you; roll the pastry away from you, firmly and evenly. If time permits, wrap the pastry roll in plastic wrap and refrigerate for about ½ hour. (This will allow for easier cutting.) Using a serrated knife and a sawing motion, slice the roll into generous ¼-inch-thick slices.
Place the slices, cut-side down, on the prepared baking sheet. Repeat with the remaining pastry. Bake the pinwheels, turning once, for about 12 to 15 minutes, or until golden brown. Transfer to a wire rack to cool.