Step 1Heat the oven to 375 degrees. Line a baking sheet with parchment paper.
Step 2Mix together the egg whites, cocoa, salt and sugar on medium speed until the batter is stiff and all ingredients are well incorporated, about 5 to 7 minutes. Stir in the walnuts or pecans by hand.
Step 3Place the batter by rounded teaspoonfuls onto the baking sheet; work in batches. Bake until the cookies are a bit shiny and slightly cracked, 10 minutes. They will look underdone but do not overbake.