Lightly grease cookie sheets with nonstick cooking spray or line sheets with parchment and then lightly grease. (Greasing is necessary even with parchment paper so that the cookies don't stick).
In a large bowl sift together the powdered sugar, cocoa powder and salt.
In a small bowl whisk the egg whites.
Stir the egg whites and vanilla extract into the dry ingredients. It will get sticky like glue.
Stir in the chocolate chips.
Drop the batter into tablespoon sized balls on the greased cookie sheet at least 2 inches apart. I like to use a cookie scoop for this.
Allow to sit on the baking sheet for 30 minutes.
Preheat the oven to 350F degrees as the cookies are resting.
Bake in the preheated oven for 7-9 minutes or until the tops look crackly.
Notes
*Store cookies in an airtight container at room temperature. **Recipe adapted from King Arthur Flour