In a large bowl, whisk flour, sugar, baking powder, baking soda, and salt until combined.
Into the the dry ingredients, pour in remaining ingredients: milk, melted butter, vanilla, and egg yolks. Whisk to incorporate and create a batter. If it seems too thick, add in an extra splash of milk.
in a stand mixer or bowl, whip your 2 egg whites until stiff peaks form. In a stand mixer you can achieve this easier, but if you're doing it in a bowl with a hand whisk sprinkle in a pinch of salt which helps the egg whites hold their form.
Once egg whites are in a firm peak, fold it gently into the waffle batter.
Preheat you Belgian waffle maker. Brush generously with melted butter and pour in the batter. Close and cook according to waffle maker instructions. If you have a double maker, shut one side of the maker, flip and fill the other section immediately so they cook at the same time.
Repeat if there's any remaining batter. Once waffles are done, top with cinnamon apples, a little maple syrup if you like and a side of bacon if you want something savory on your plate!