1. Heat the milk in the microwave until warm. Stir in the melted butter.
2. Whisk together the flour, sugar, yeast, cinnamon, and salt in a large bowl. Gradually whisk in warm milk and butter until smooth. Whisk in the eggs and vanilla until incorporated. Scrape down sides of bowl, cover and refrigerate 12-24 hours.
Heat the waffle iron. When the iron is hot, remove batter from refrigerator and whisk to recombine and deflate. Spread the correct amount of batter onto waffle iron and cook until golden brown, about 3-4 minutes. Repeat with remaining batter or put batter in fridge to use again the next day. Mine usually lasts about 3 days.