Whisk the flour, sugar, cinnamon, baking powder, and baking soda together in a large bowl.
Separate the egg whites from the egg yolks and set them aside.
Combine the buttermilk, milk, melted butter, and egg yolks in a separate bowl and whisk until combined.
Add the wet ingredients to the dry ingredients and combine until no lumps appear.
Using an electric mixer, or by hand, whisk the egg whites until they’re light and airy and stiff peaks form. Fold the egg whites into the batter.
Carefully stir in the blueberries until just combined.
Allow the batter to sit for 30 minutes while you warm up the waffle iron. (This step is optional, but allows the flour to fully hydrate, allowing the batter to cook more evenly.
Preheat your waffle iron. Add ¼ - ½ cup of batter to the waffle iron (depending on how big yours is) and cook until crispy on the outside. (My waffle maker typically takes about 4-5 minutes for each waffle).
Serve immediately with toppings. Waffles can also be frozen and reheated in the toaster for a quick weekday breakfast.