Ingredients
2 3/4 cups (275g) walnut halves
3 cups (350g) confectioners' sugar
1/2 cup plus 3 tablespoons (70g) Dutch-processed cocoa powder
1/4 teaspoon kosher salt
4 large egg whites, at room temperature
1 tablespoon pure vanilla extract
Instructions
  1. Heat the oven to 350°F (175°C), with racks in the upper and lower thirds. Spread the walnut halves on a large rimmed baking sheet and toast in the oven until they turn golden and smell toasty, about 9 minutes.
  2. Let the walnuts cool to the touch, then transfer them to a cutting board and coarsely chop them. Line two large rimmed baking sheets with parchment paper or silicone baking mats.
  3. Combine the confectioners’ sugar, cocoa powder, salt, and walnuts in the bowl of a stand mixer fitted with the paddle attachment. Mix on low speed until well combined. With the mixer running, slowly add the egg whites and vanilla. Mix on medium speed until the mixture has just slightly thickened, about 3 minutes.
  4. Using a 2-ounce (60ml) cookie scoop or a large spoon, scoop the batter onto the baking sheets in 12 mounds, spacing them 3 inches (7.5cm) apart. Put the baking sheets in the oven, immediately lower the temperature to 325°F (165°C), and bake until the tops are glossy and lightly cracked, 14 to 16 minutes, rotating the baking sheets from front to back and top to bottom halfway through baking. Slide the parchment paper (with the cookies) onto two racks to let the cookies cool completely before removing the cookies from the parchment. Store in an airtight container at room temperature.