Makes 10 waffles

8     tablespoons (150g) unsalted butter - melted and cooled
1 1/2 cups water (375ml) (divided)
2 1/4 teaspoons (one packet) active dry yeast
3     cups (300g) sifted flour
1/4   teaspoon salt
3     large eggs, separated + 1 egg white
1/3   cup (50g) sugar
1 1/2 cups (375ml) whole milk
2     teaspoons vegetable oil
2     teaspoons pure vanilla extract

Heat half of the water to lukewarm, 105-110F (40-45C). Dissolve the yeast in the water with a pinch of the sugar from the recipe; let stand 5 to 10 minutes, until the mixture begins to foam.

Put the flour and salt into a large bowl; stir to blend and reserve. Add the egg yolks, one of the egg whites, and remaining sugar to the yeast mixture; stud to blend. Add the remaining water, milk, melted butter, oil, and vanilla; stir until the mixture is smooth. Stir the liquid mixture into the flour mixture and beat until the mixture is smooth.

Beat the egg whites until stiff peaks form. Fold the egg whites gently into the batter. Let the batter stand for 1 hour, stirring every 15 minutes.