The night before: Pour warm water in the bottom of a large bowl. Sprinkle yeast on top and let it dissolve for 15 minutes.
Stir in milk, butter, salt, sugar, and flour. Cover the bowl with plastic wrap and set out on the counter overnight.
The next morning, whisk in eggs and baking soda until smooth.
Heat waffle iron and coat lightly with butter or oil. Ladle in ½ to ¾-cup batter per waffle batch.
Waffles can be kept crisp in a warm oven until needed. If you only want to make a few at a time, the batter keeps well in the fridge for several days.
