Heat waffle iron.
Separate the egg yolks and egg whites into two separate bowls.
Whisk dry ingredients together in a medium bowl. Whisk the egg yolks with the butter milk and butter.
Beat the egg whites with a hand mixer or a whisk until the whites hold a stiff peak.
Add the wet ingredients to the dry ingredients slowly while gently mixing with a rubber spatula. You do not want to add the liquid ingredients faster than you can incorporate them into the dry ingredients! Gently fold in the egg whites into the batter until just combined then fold in the blueberries.
Spread a ¼ to ½ cup of the batter onto the waffle iron and cook until golden brown, about 2 to 5 minutes.
Note: Every waffle iron is different so your cooking time might vary! Additionally, different irons can yield a different number of waffles at a time so if you have a single, or a double, or a quad like I do, portion the batter so you yield 6-8 waffles.
Serve with butter, maple syrup, and top with additional blueberries. Enjoy!