Preheat the oven to 350°F.
Add the powdered sugar, cocoa powder, egg whites, vanilla, and salt to a large bowl. Mix until fully combined and no lumps of powdered sugar or cocoa remain. The batter should look like a very thick brownie mix.
2 large egg whites, 2 cups powdered sugar, ½ cup unsweetened cocoa powder, 1 teaspoon vanilla bean paste, pinch of salt
(Optional) Gently fold in your add-ins until evenly distributed.
¼ cup dark chocolate chips, ¼ cup white chocolate chips, ¾ cup almonds
Line a baking sheet with parchment paper or a silicone baking mat. Divide the dough into 6 portions, spacing them well apart. The cookies spread as they bake, so use two sheets or bake in two batches.
Bake for 18 to 22 minutes, depending on how chewy you like your cookies. You should see cracks form across the surface, and the centers should still be fudgy. I bake mine for 20 minutes.
Let the cookies cool completely on the pan before removing them. They set more as they cool.