►Grease waffle iron and heat according to manufacturer’s settings. Heat oven to 250°F.
►Combine flour, cornstarch, baking powder, baking soda, and salt in a small mixing bowl.
►Whisk egg yolks, milk, ricotta, sugar, lemon juice, and lemon zest in a large mixing bowl until well combined. Slowly whisk in melted butter and stir until fully incorporated. Add dry ingredients to the egg-ricotta mixture and stir until just combined.
►Whip egg whites in the bowl of a stand mixer fitted with the whisk attachment (or a large bowl with an electric mixer) on medium-high speed until soft peaks form. Use a rubber spatula to fold in the egg whites into the batter until just incorporated.
►Dollop batter into prepared waffle iron (a little less than ¹⁄³ cup for a 4-inch grate) and cook until golden brown and crispy. You will know waffles are ready when the steam escaping the iron stops. Place on a baking sheet in an even layer and keep warm in the oven while you finish cooking.
Waffles that have been toasting can be stacked to make room for new batches. Serve immediately garnished with blueberries, maple syrup, and powdered sugar.