Adapted from King Arthur Flour
2 1/4 cups powdered sugar
1/4 teaspoon salt
1 teaspoon espresso powder
1 cup Dutch process cocoa powder
3 egg whites
2 teaspoons vanilla
2 cups chocolate chips, wafers or chunks
Preheat oven to 350º. Line cookie sheets with parchment or Silpats.
Stir all ingredients together except chocolate chips. Mixture will eventually come together. Scrape bowl and mix again. Stir in chocolate chips.
Use a tablespoon cookie scoop to drop batter onto prepared cookie sheets. Reshape if necessary.
Bake for 8 minutes, till shiny with a few cracks on top. Allow to cool completely on pan, then remove to rack.