1Preheat a waffle iron according to manufacturer's instructions. Prepare the cooking surface with cooking spray.
2Beat flour, milk, eggs, vegetable oil, baking powder, and salt together in a bowl using an electric mixer until batter is thoroughly mixed.
3Pour about 1/4 cup batter per waffle into the preheated waffle iron and cook according to manufacturers' instructions.
4Stir blackberries together in a saucepan over high heat until heated through, 3 to 4 minutes. Decrease heat to medium and add sugar, cornstarch, and lemon juice to blackberries; cook and stir until sauce is thickened, about 5 minutes.
Footnotes
Cook's Note:
If you have a big sweet tooth, add more sugar to the sauce. If you want a more flavorful waffle batter, add 1 tablespoon ground cinnamon, and 1 teaspoon vanilla extract.