Preheat the waffle iron, coat with nonstick spray, and keep it ready.
In a large mixing bowl, combine the flour, cocoa powder, baking powder, baking soda, sugar, salt, and cinnamon by whisking thoroughly.
Using a hand mixer, beat the egg whites in a separate bowl until they form stiff peaks, then set aside.
In another medium-sized bowl, blend together the egg yolks, milk, coffee (or milk if substituting), vegetable oil, and vanilla extract until smooth.
Pour the egg yolk mixture into the bowl with the dry ingredients and stir until fully incorporated.
Gently fold the stiff egg whites into the batter, ensuring a light and airy consistency.
Spoon the prepared batter into the preheated waffle iron and cook following the manufacturer's instructions until crisp and cooked through.
Serve promptly, garnished with butter, syrup, powdered sugar, or your preferred toppings.