Grease a 8"x8" baking dish with butter or cooking spray.
In a medium bowl bowl, whisk together the flour and cocoa powder. Set aside.
In a separate bowl, whip the egg whites with vinegar until stiff peaks form. Set aside.
In a third bowl, beat the egg yolks and sugar until pale yellow in color (it will still be grainy). Beat in the melted butter, espresso powder and vanilla extract until evenly incorporated. Mix the flour mixture into the batter until evenly incorporated. Add the milk and beat low speed. Gradually and gently fold in the egg whites. Pour the batter into the prepared pan and bake for 50-60 minutes or until the cake is slightly jiggly.
Cool completely. Dust with powdered sugar and garnish with fresh berries.
Recipe by The Best Video Recipes for All at https://recipes-for-all.com/chocolate-magic-cake/