In a large bowl, combine the flour, sugar, cornstarch, baking powder, baking soda, and salt. In a separate bowl, whisk together the buttermilk, eggs, melted butter and vanilla. Add the buttermilk mixture to the dry ingredients and stir until just combined.

Preheat a waffle maker according to manufacturer's instructions. Grease with non-stick spray if necessary. Pour scant 1 cup batter into the hot waffle maker (1/2 cup for smaller waffle irons). Cook until golden brown (this was about 5-6 minutes in my waffle iron.)

Serve immediately, or keep warm in a 200 degree F oven in a single-layer.