In a bowl, whisk together the flour, cornstarch, sugar, baking powder, baking soda, and salt. Add the milk, oil, egg and vanilla and mix well. Let the batter sit for 30 minutes.
Preheat a waffle iron but don't spray it with nonstick spray; the oil in the batter will allow the waffle to release easily. Cook them according to the waffle maker's directions, and serve warm.