In a bowl combine the flour, baking powder, cornstarch, and salt; whisk to combine. Add egg, sugar, milk, water, and vanilla. Gradually whisk the ingredients until well combined, then whisk in the melted butter.Spray each side with oil. Pre-heat Waffle Puff Pan on medium heat for 3 minutes. Add ¾ cup of waffle batter filling in all the bubbles. Flip the waffle maker over and cook for 2-4 minutes. Flip the waffle maker again and cook for 2-4 minutes or until golden brown. Remove with Fork and let rest 1 minute to allow the bubble waffle to crisp. Then top with your favorite toppings.