First, add the flour, cocoa powder, and baking powder into a sifter and sift into a large mixing bowl. Once it is all sifted into the bowl, add the salt and granulated sugar and use a metal whisk to fully combine.
In a large electric mixer, whip the egg whites until completely fluffy, like a meringue. They should be bright white and fluffy, like clouds.
In a medium mixing bowl, whisk together the melted butter, egg yolks, and milk until fully combined. Add the wet ingredients to the large bowl with the dry ingredients and use a silicone spatula to mix together until smooth.
Add the whipped egg whites to the batter and gently fold into the rest of the batter until smooth. DO NOT mix vigorously, as this will knock ALL the air out of the meringue and the batter will fall.
Cook according to the directions on your waffle iron, then serve fresh dusted with powdered sugar. Enjoy!