How to Make It
Preheat the oven to 200°. In a medium bowl, combine the flour, cornstarch, salt, baking powder and baking soda. In a glass measuring cup, blend the buttermilk, vegetable oil and milk. Beat in the egg yolk.
In a medium bowl, beat the egg white to soft peaks. Add the sugar and beat until firm and glossy. Beat in the vanilla.
Pour the liquid ingredients into the dry ingredients and whisk until just blended. Using a rubber spatula, gently fold in the beaten egg white until just incorporated.
Preheat an 8-inch square waffle iron and oil it lightly. Pour about 1 1/2 cups of the waffle batter into the preheated waffle iron and gently smooth the surface with a spatula. Bake for 4 minutes, or until browned and crisp. Transfer the waffles to the oven rack to keep warm and repeat with the remaining batter. Serve at once with maple syrup.