Sift the flour, sugar, baking powder, and baking soda together in a bowl.

In a separate bowl, beat the egg yolks and buttermilk together.

Gradually add the dry ingredients to the wet ingredients, alternating with the melted butter, cooled to room temperature.

Stir until the batter is smooth and free from lumps.

In a separate bowl, beat the egg whites until stiff peaks form.

Gently fold the beaten egg whites into the batter.

Preheat a Belgian waffle iron according to manufacturer's instructions.

Pour the batter onto the preheated waffle iron.

Bake until the waffles are golden brown and cooked through, usually 3-5 minutes.

Serve immediately.