In a large bowl, whisk together flour, cornstarch, sugar, baking powder, baking soda, and salt until well combined.
Make a well in the center of dry ingredients. Add egg yolks, buttermilk, melted butter, and vanilla. Mix until just combined—some small lumps are fine.
In a separate bowl, beat egg whites until stiff peaks form. This creates the signature crispy outside and fluffy inside texture.
Gently fold whipped egg whites into the batter using a spatula. Be careful not to deflate the air bubbles.
Preheat your waffle iron to medium-high heat according to manufacturer instructions. Lightly grease with cooking spray or butter.
Pour enough batter to cover about two-thirds of the waffle iron surface. Close the lid and cook for 4-6 minutes until deeply golden and steam has mostly stopped.
Transfer waffles immediately to a wire rack. For extra crispness, keep finished waffles in a 200°F oven on a wire rack while cooking remaining batches.
Serve hot with maple syrup, butter, fresh berries, or your favorite toppings. Enjoy immediately for best texture.