Add in the egg whites and combine the batter until smooth and there are no lumps. It will appear at first that there isn't enough liquid, but keep persisting and the batter will come together as a thick, sticky texture (see picture for consistency)
2 Egg whites
Scoop large tablespoon sized batter onto the cookie sheet. A teaspoon can help here to separate the sticky batter mixture from your spoon.
Bake for 15-17 minutes (mine are perfect at 16 minutes). The brownie cookies will have appear shiny and puffy, with a gooey looking inside.
Allow cookies to set on the tray for a couple of minutes.