Line two baking sheets with silicone baking mats. Spray mats with nonstick cooking spray. You can also line with parchment paper.
In a large bowl, whisk together the powdered sugar with cocoa powder and salt.
Stir in the vanilla and egg whites.
Whisk just until the batter is moistened.
Stir in the chocolate chips.
Scoop the batter by the tablespoonful onto the baking sheets. The batter will be thin. Leave enough space between each cookie for them to spread (about 2 ½” of space between each cookie).
Bake for 8-10 minutes, or until the tops are glossy and lightly cracked.
Let the cookies cool completely on the baking sheet, and store in an airtight container for up to 3 days.
Some people have found that they have better luck with 3 egg whites and other people have found that the recipe works better with 4. You may want to start with 3 egg whites, and add the 4th egg white if needed.
You can swap out part or all of the vanilla for other extracts and flavorings, like peppermint, to change up the flavor.