Preheat waffle iron according to manufacturer's instructions. In a large bowl, add flour, sugar, baking powder, and salt. Whisk together until combined. Set aside.
In a medium bowl, add egg yolks, milk, oil, and vanilla extract. Whisk together to combine. Add to dry ingredients and whisk together just until combined.
Beat egg whites until soft peaks form. Add to batter and gently fold in just until combined.
Spray nonstick spray on preheat waffle iron. Add batter to waffle iron and cook according to manufacturer's instructions. My small round iron held ⅓ cup of batter but yours could hold more or less depending on the size of the iron. Repeat with all of the batter.
Place melted butter in a shallow dish. Add cinnamon and sugar to another shallow dish and stir together. Dip one waffle into the melted butter and let as much of the excess butter drip off as possible. Dip into cinnamon sugar and quickly flip to coat the other side. Repeat with other waffles