In a large bowl, whisk together the flour, cornstarch, salt, baking powder and baking soda. In a separate bowl, whisk together the buttermilk, milk, vegetable oil, egg yolk and vanilla.
In a small bowl using a hand mixer beat the egg white and sugar until stiff peaks form.
Add the buttermilk mixture to the flour mixture and stir until a smooth batter forms. Add the beaten egg white with sugar to the batter and gently fold in with a spatula until well combined.
Heat a waffle iron and make the waffles according to manufacturers instructions. Served immediately with butter and syrup.