Preheat. Preheat your waffle iron. If you want to keep waffles warm, heat oven to 200F and place a wire rack on a sheet pan.
Mix dry ingredients. In a large bowl, whisk flour, cornstarch, sugar, baking powder, and salt.
Mix wet ingredients. In a second bowl, whisk egg yolks, milk, melted butter, and vanilla until smooth.
Combine. Pour wet ingredients into dry and stir gently until just combined. Do not overmix.
Whip egg whites. In a clean bowl, beat egg whites until soft peaks form.
Fold in egg whites. Gently fold whipped egg whites into the batter until mostly combined (a few streaks are fine).
Cook waffles. Lightly grease the waffle iron if needed. Add batter and cook according to your waffle maker until deeply golden and crisp.
Serve. Serve immediately, or keep warm on the oven rack while you cook the rest.
