1. Preheat waffle iron.  
2. In a large bowl, whisk together flour, cocoa, sugar, baking powder, baking soda and salt. 
3. Create a well in the center of the flour mix and pour in egg yolks, milk, oil and vanilla. Whisk until blended and smooth. Set aside. 
4. Using a stand mixer fitted with a whisk attachment, beat the egg whites until stiff peaks form. Add the whites to the batter and fold until blended. Sprinkle in the chopped chocolate and fold those in as well, until blended with the batter. 
5. Lightly grease your waffle iron with pan release spray and, using a 1/4-1/2 cup measure (depending on the size of your waffle iron), ladle in the batter. Cook until fluffy and thoroughly cooked through. 
6. Remove from the iron, place on a wire rack and set aside. Repeat, using all the batter. Sprinkle waffles with powdered sugar before serving.