Preheat oven to 350°F (177°C). Line an 8 x 4 inch baking pan with parchment paper.
Add cocoa powder and allulose to a large mixing bowl. Mix together with a whisk until evenly combined and there are no lumps of cocoa or allulose.
Add in egg whites. Whisk in egg whites until the 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 continue to absorb the dry ingredients and will turn into a thick batter.
Pour batter into the prepared baking pan. Bake for about 20-25 minutes. Mine took 23 minutes. When brownies are done, the surface should be puffed up and look cooked (it shouldn't look wet). Let brownies cool fully before cutting and serving. As the brownies cool, they will deflate because of how fudgy they are. The brownies are very fudgy and will stick to the bottom of the parchment paper. I recommend using a thin silicone cookie spatula (the kind of spatula that is used to remove or turn the cookies, not the spatula used for mixing batter) to remove the brownies off the parchment paper.
