Preheat the oven to 350°F (175°C). Line a large rimmed baking sheet with parchment paper or silicone baking mats. If you are using parchment paper, spray it with cooking spray.
In a large bowl, whisk together the powdered sugar, cocoa powder, and salt.
Add the vanilla extract, the egg white, and whisk until you obtain a thick but moist batter. IF it seems too thick, add another egg white.
Fold in the chocolate chips.
Using a cookie scoop or a large spoon, scoop the batter onto the prepared baking sheet. Leave enough space between each cookie as they will spread a bit.
Bake for 12-14 minutes, until the tops are glossy and they begin to crack.
Let the cookies cool completely before removing them from the baking sheet with a spatula.
Notes
Egg whites - Don’t add that 2nd egg white too soon – it takes time for the dry mix to start absorbing the egg.
Storage - Store cookies in an airtight container at room temperature for up to 3 days or freeze them for up to 3 months.