Preheat the oven to 180°c and line 2-4 rimmed baking trays with parchment paper.
Sift the powdered sugar and cocoa powder into a large bowl and whisk to combine.
Stir in the egg whites, vanilla extract, and salt. Mix until all the sugar/cocoa is moistened. Then stir in the chocolate chips.
Using a medium ice cream scoop (1½ tablespoons), scoop the cookie batter onto 2 of the prepared baking trays, leaving plenty of room between cookies for spreading. We recommend no more than 8 cookies per baking tray.
Bake the first tray of cookies on the centre and lower rack for about 14 minutes, rotating halfway through. The cookies are done when the tops are glossy and crackly, and the edges are set. Repeat with the remaining cookie dough on the remaining trays, as needed.
Cool the cookies completely on the baking pans on a wire rack.
Store the cookies in an airtight container for up to 3 days.