In a small sauce pan, heat the milk and butter over medium heat. When about half of the butter has melted, off the heat and continue stirring until the rest of the butter melts. Let cool until warm to the touch, about 105°F to 110°F.
In a large bowl, whisk together the flour, sugar, yeast, and salt until combined. Set aside.
In a small bowl, whisk together the eggs and vanilla in a small bowl. Set aside.
Slowly pour the warm milk into the flour mixutre and whisk until incorporated. Stir in the egg mixture until a thick batter forms.
Loosely cover with plastic wrap and place in a warm and draft-free environment* until doubled in size with bubbles on the surface, about 60 minutes.
Give the risen batter a large stir, just to deflate, and cook in the waffle iron according to manufacturer instructions.