Preheat the oven to 200° F and preheat a waffle iron. Whisk the flour, baking soda, baking powder, and salt in a large bowl to combine.

Combine the melted butter and brown sugar in a separate large bowl. Whisk in the egg yolks and buttermilk. Mix the cocoa powder and red food coloring in a small bowl to make a smooth paste, then whisk the paste into the butter mixture. Stir the wet ingredients into the dry ingredients just until moistened (the batter should be slightly lumpy).

Beat the egg whites in a medium bowl with an electric mixer until stiff peaks form. Stir one-quarter of the egg whites into the batter to lighten it. Then fold in the remaining egg whites gently but thoroughly.

Spray a waffle iron with nonstick cooking spray or brush with melted butter. Cook the waffles according to the manufacturer’s instructions. As they’re done, put them on a baking sheet and slide them into the oven to keep them warm while you cook the remaining waffles.