Preheat your oven to 350°F (175°C). Line two rimmed baking sheets with parchment paper or silpat mats. If you’re using parchment paper, give it a light coating of nonstick spray to ensure easy removal.
In a large bowl, whisk together the powdered sugar with the Dutch process cocoa powder and salt. Make sure there are no lumps in the dry mixture.
Gradually whisk in the egg whites, starting with just two. Add the vanilla extract and mix until the batter is moistened. You want a thick, fudgy batter that resembles brownie batter.
If the mixture feels too thick, add another egg white and mix again. If it still seems too thick after this, add a fourth one.
Gently fold in the bittersweet chocolate chips with a spatula, ensuring they are evenly distributed throughout the batter.
Using a spring-release cookie scoop, spoon the batter onto the prepared baking sheets. Space them about two inches apart to allow for spreading.
Bake the cookies for about 14 minutes, until the tops are glossy and lightly cracked.
Once baked, carefully slide the parchment paper with the cookies onto wire racks to cool. This will help them maintain their chewy texture.
Let the cookies cool completely before attempting to remove them from the parchment. They are delicate, so gently peel away the paper.
Store any leftover cookies in an airtight container for up to three days, if they last that long!