For cakes, preheat oven to 350°F. Grease six 2 1/2-inch muffin cups. Set aside. In a medium bowl whisk together flour, cocoa powder, baking soda, and salt. In another medium bowl whisk together egg whites, brown sugar, the remaining 2 tablespoons granulated sugar, the milk, oil, and vanilla. Add all at once to the flour mixture. Whisk until well combined. Spoon evenly into prepared muffin cups.