Step 1

Preheat oven to 350°F. Line an 8 ½ inch by 4 ½ inch baking pan with parchment paper.

Step 2

Add cocoa powder and powdered sugar to a large mixing bowl. Mix together with a whisk until evenly combined.

Step 3

Add in egg whites. Whisk in egg whites until batter becomes smooth and thick. Because this batter has very little liquid, it may seem like you don't have enough liquid at first but as you continue to incorporate the egg whites into the dry mixture, it will turn into a thick batter. See recipe notes for more tips.

Step 4

Pour batter into prepared baking pan. Bake for about 20-25 minutes. Insert a toothpick to check for doneness. The batter should not be liquid but the crumbs will stick to the toothpick when the brownies are ready. As the brownies cool, they will shrink. See notes for tips for keeping the brownies from shrinking too much when they cool. Let brownies cool fully before cutting and serving.