Step 1

1 Place racks in the upper and bottom thirds of the oven and preheat to 350 degrees

Step 2

2 Line two baking sheets with parchment paper or silicone baking mats

Step 3

3 Combine the cocoa powder, confectioners' sugar, salt and walnuts in the bowl of a stand mixer fitted with the paddle attachment

Step 4

4 Beat on low speed for 1 minute

Step 5

5 With the mixer running, slowly add the egg whites and vanilla extract

Step 6

6 Beat at medium speed for 3 minutes, until the mixture has thickened slightly and looks lumpy

Step 7

7 Do not overmix, or the egg whites will thicken too much

Step 8

8 Use a 2-ounce cookie or ice-cream scoop, or a generous tablespoon, to scoop the batter onto the prepared baking sheets

Step 9

9 Scoop 5 cookies onto each sheet, spacing them about 3 inches apart so that they don't stick when they spread

Step 10

10 If you have extra batter, wait until the first batch of cookies is baked before scooping the next batch

Step 11

11 Transfer the baking sheets to the oven and immediately reduce the temperature to 320 degrees

Step 12

12 Bake for 15 to 20 minutes, rotating the pans front to back and top to bottom about halfway through baking; small, thin cracks will appear on the surface of the cookies

Step 13

13 Pull the parchment paper with the cookies onto a wire cooling rack, and cool completely before removing the cookies from the paper

Step 14

14 NOTE: To toast the walnuts, spread them on a baking sheet and place in a 350-degree oven, shaking the sheet occasionally, for 8 to 10 minutes

Step 15

15 Watch carefully; nuts burn quickly