Whisk together:
1 envelope (2 1/4 teaspoons) active dry yeast
1/4 cup warm (105° to 115°F) milk
Let stand until the yeast is dissolved, about 5 minutes. Whisk together in a large bowl:
3 large egg yolks
1/4 cup lukewarm milk
12 tablespoons (1 1/2 sticks)
unsalted butter, melted and cooled to lukewarm
Whisk in the yeast mixture along with:
1/2 cup sugar
1 1/2 teaspoons salt
2 teaspoons vanilla
Add, in 3 parts:
4 cups all-purpose flour
alternating, in 2 parts, with:
2 1/2 cups warm (105° to 115°F) milk
Beat until soft peaks form then fold into the batter: 3 large egg whites
Cover the bowl tightly with plastic wrap and let rise in a warm place until doubled in volume, about 1 hour. Stir to deflate the batter.
Preheat your waffle iron.
Spoon 1/2 cup batter (or the amount recommended by your waffle iron's manufacturer) onto the hot iron. Spread the batter to within 1/4 inch of the edge of the grids, using the back of a metal spatula, wooden spoon, or ladle. Close the lid and bake until the waffle is golden brown. Serve immediately or keep warm in a single layer on a rack in a 200°F oven while you finish cooking the rest. Serve with:
Pats of butter and powdered sugar or fresh fruit and whipped cream.
