Preheat oven to 350℉ (convection bake, if you have it)
Prepare sheet pans by lining with parchment paper. It will take atleast 2 pans, likely 3 depending on the size of your pans.
Crack egg whites into your mixing bowl and add vanilla extract. Your egg whites should be room temperature. If you forget to pull ahead of time, you can place the whole egg (in the shell) in a bowl of warm water for 5-10 mintues.
Sift cacao powder, powdered sugar and salt into the bowl on top of egg whites.
Add chocolate chips to the bowl.
Using a rubber spatula, mix only until the batter is creamy and smooth.
Scoop batter with a 2TBSP cookie scoop onto your prepared sheet pan. Leave 3-4 inches between each cookie as they spread quite a bit during baking. I try to ration the chocolate chips in each scoop, spreading them out within my batter. Otherwise, you are left with all all liquid batter and no chocolate chips in your last couple of scoops.
Bake 14 minutes, rotating halfway through to ensure even baking. The cookies should be a smooth, shiny crackled exterior with a gooey, chewy center. If you find that your cookies are still fragile after they have cooled, you may need to increase your bake time by 2-3 mintues. Because ovens vary so much, I always recommend starting with the shorter bake time on the first batch.
Allow to cool completely before attempting to remove from parchment paper as they are very fragile while warm
Store at room temperature in an air tight container for up to 10 days.