Preheat oven to 350°F (175°C).
Line two baking sheets with parchment.
Whisk powdered sugar, cocoa, and salt.
Add egg whites and vanilla.
Stir until you've got glossy brownie batter, not cookie dough.
Pro tip: Whip the egg whites with the sugar first until dissolved, then fold in cocoa and salt. Crackly tops guaranteed. A blender or stick blender works too.
Stir in chocolate chips.
Portion 2 tablespoons per cookie on sheets. Leave space. They spread.
Chill dough 30 minutes first if you want taller cookies with that brownie crust.
Bake for 10 minutes. Tops should be shiny and cracked.
Cool 5 minutes on the sheet. Move to a rack.
