Preheat oven to 350℉. Line baking sheets with parchment and lightly spray cooking spray, not flour cooking spray. I do not recommend a silicone baking mat here.
Stir together the powdered sugar, cocoa powder, salt, egg whites, and vanilla extract. Mix well, scraping down the sides of the bowl. It will take some time for the mixture to come together.
Add the chocolate chips and mix them in completely, trying to get them distributed in the cookie batter.
Using a medium cookie scoop, drop cookie batter onto the prepared baking sheet.
Bake until the tops are slightly cracked and glossy, about 15 minutes. Remove the baking sheet from the oven and place on a wire rack. Cool the cookies completely on the baking sheet.
The cookies are fragile when warm. They set just a bit when cool and you will have to peel the parchment paper from the back of the cookie for best results. Do this gently. Place cookies on a wire rack until ready to store in an airtight container.