01 -
In a large bowl, whisk together the flour, granulated sugar, cornstarch, and kosher salt until well blended.
02 -
Cut the butter into small pieces and place in a saucepan with half of the milk. Warm over medium heat until the butter is nearly melted and the milk is just beginning to bubble at the edges, 2 to 4 minutes. Remove from heat and let the residual heat finish melting the butter, 1 to 3 minutes. Whisk in the remaining milk.
03 -
Separate the egg whites into a clean, dry medium bowl and yolks into a small bowl or measuring cup. Whisk the egg whites until stiff peaks form, approximately 4 minutes. If using, add vanilla extract to the yolks and whisk until fully combined.
04 -
Add the egg yolk mixture to the warm milk mixture and whisk until smooth.
05 -
Pour the liquid mixture into the bowl with the dry ingredients and stir until just combined. It's normal for the batter to be a little lumpy; avoid overmixing.
06 -
Gently fold stiff egg whites into the batter with a flexible spatula, just until no streaks remain. Do not overmix.
07 -
Preheat waffle iron to medium-high setting according to manufacturer instructions. A drop of water should sizzle on contact.
08 -
Coat the waffle iron with cooking spray. Pour approximately 120 millilitres (1/2 cup) of batter per waffle or as specified by manufacturer. Spread to cover the surface. Cook 3 to 5 minutes or until golden-brown. Remove, allow the iron to reheat for 2 to 3 minutes before making the next batch.
09 -
Serve immediately with additional butter and maple syrup, or keep warm on a wire rack set over a rimmed baking sheet in a 90°C oven for up to 15 minutes.