Add water to a large mixing bowl (batter will rise to double its original volume), sprinkle in the active-dry yeast, and let stand 5 minutes to proof. (This waiting time is not necessary with instant yeast.)

Stir in the milk, butter, sugar, salt, and flour. Cover the bowl an let sit out at room temperature overnight.

Heat waffle iron. If you want to serve the waffles all at once, set a rack inside a rimmed sheet pan, put it in a 300°F oven, and as you make the waffles, transfer them here.

Separate the eggs and whip whites to stiff peaks either by hand or with an electric mixer. Set aside.

In a small bowl, whisk yolks with baking soda, gently stir into the batter, then fold in the egg whites.

Brush melted butter on the waffle iron plates, if desired. Scoop batter with a half-cup measuring cup, pour into center of the plates, close the lid, and cook until golden brown and crispy.

On the Chef's Choice 830B waffle iron, I set the doneness to 5 (from 1 to 6) and use the "uniform texture" switch for the most crisp results (versus "crisp outside and moist inside" which seems to steam the crispness right out of the waffle as it rests).