Preheat your waffle iron according to the manufacturer's instructions.

In a large bowl, whisk together the flour, sugar, baking powder, and salt.

In another bowl, beat the egg yolks. Add the milk, oil, and vanilla extract, mixing well.

Add the wet ingredients to the dry ingredients and stir until just combined.

In a separate bowl, beat the egg whites until stiff peaks form. Fold the egg whites into the batter gently.

Pour the batter onto the preheated waffle iron and cook until golden brown and crisp.

For the blueberry sauce, combine the blueberries, sugar, and lemon juice in a saucepan over medium heat.

Bring to a simmer and cook for about 5 minutes, until the blueberries begin to break down.

Stir in the cornstarch mixture and cook for another 1-2 minutes until thickened.

Serve the waffles warm, topped with the blueberry sauce.