(The night before)
1. Combine yeast with 1/2 c. warm water; stir to combine.
2. Melt butter in a large (3 qt) microwave-safe bowl.
3. Pour 1 cup of milk into the melted butter and stir to combine. Cool to 110 degrees or less (just above room temperature) if needed.
4. Add yeast mixture, sugar, salt and flour to bowl; whisk or beat until there are no lumps.
5. Cover lightly with plastic wrap and leave batter at room temperature overnight.
(The next morning)
6. Heat your waffle iron.
7. Separate the eggs and put the yolks into the waffle batter. Whisk until completely combined.
8. Beat the egg whites with a hand or stand mixer until soft peaks form.
9. Gently fold the egg whites into the waffle batter until completely combined.
10. Pour batter into waffle iron to prepare waffles as per manufacturer's directions.
Good to know
This recipe makes 5-6 one-serving belgian waffles; yield will vary based on size of waffle iron.
You should not need to grease the waffle iron; my (modern) waffle iron is non-stick but even the original recipe did not require the waffle iron to be greased.
Note that if you don't mind a flat waffle, you can skip the step of whipping up the egg whites in the morning; just whisk two eggs into the waffle batter and cook the waffles.
The original recipe contained baking soda which I've left out; it appears to have no effect.
Leftover batter can be refrigerated and made into waffles up to 3 days later.
For a slightly heartier waffle, substitute a cup of either whole wheat or buckwheat flour for one cup of the flour in the recipe.