2 large egg yolks
1 1/2 cups whole milk
2 teaspoons baking powder
1 1/4 cups all purpose flour
1/4 cup unsweetened cocoa powder
4 tablespoons unsalted butter, melted
2 large egg whites
2 tablespoons light brown sugar

Heat waffle iron and spray with nonstick cooking spray.
In a medium bowl, combine the egg yolks, milk, baking powder, flour, cocoa powder and melted butter until almost smooth and set aside. In the bowl of an electric mixer fitted with the whisk attachment, whip egg whites until stiff peaks form. Add the brown sugar and continue whopping until stiff. (You are done when you lift the bowl over your head and the egg whites do not move from the bowl.) Lightly fold the whipped egg whites into the batter.
For each waffle, pour the amount recommended by the manufacturer and bake as directed. Top with pure maple syrup.