Add flour, yeast, sugar and salt to a large mixing bowl.
Whisk in the milk until well combined, then cover the bowl tightly with plastic wrap. Let stand overnight, at room temperature.
The next morning, plug in your waffle iron and bring it up to high heat (or until your 'ready' light appears, depending on your manufacturer).
Lightly beat the egg and melt the butter, then add both to the batter and whisk to combine (it will be a thin batter).
Spray the hot waffle iron with nonstick spray and pour about 1 cup of batter into the hot iron. (Tip: spread the batter into the corners with an offset spatula, in order to get a fully square waffle.)
Cook until nicely browned (approx. 2-3 minutes). Serve with maple syrup (and sauteed peaches, if desired).