In a medium bowl, whisk together flour, cornstarch, baking powder, baking soda, and salt.
Drain peaches, reserving 1/4 cup liquid. Mix buttermilk, melted butter, egg, sugar, cinnamon, vanilla and 1/4 cup peach juice until combined. Add to the dry ingredients.
Dice sliced peaches into chunks. Pat dry with paper towels to prevent the waffles from getting soggy. Fold the peaches into the batter. Let sit for 30 minutes.
Pour batter into preheated waffle iron. Cook for 4 to 5 minutes.
