Preheat the oven to 320.

Line three (preferably rimmed) baking sheets with parchment paper. Or you can bake in batches with fewer pans.

Make sure your walnuts have cooled a bit, then chop coarsely and set aside. Sift together the confectioner's sugar, cocoa powder, and sea salt.

Stir in the walnuts, then add the egg whites and vanilla. Stir until well combined.

Spoon the batter onto the prepared sheets in mounds of about 2 tablespoons each, allowing for plenty of room between cookies. Don't try to get more than 6 cookies on each sheet, and try to avoid placing the batter too close to the edge of the pan

Bake about 12-15 minutes.

Slide the cookies still on parchment onto a cooling rack, and let them cool completely.