Sprinkle yeast and 1 tbsp. sugar into a medium bowl; pour 1/2 cup warm (110°) water over them. Stir and let stand until foamy, about 8 minutes. Add milk, butter, and flours, then whisk until smooth. Cover bowl with plastic wrap and let rise overnight on the counter (for slightly sour waffles) or chill (for sweet waffles).
In the morning, preheat oven to 200° and set 6 plates on a rack. Preheat a Belgian or regular waffle iron. Add eggs, baking soda, salt, and vanilla to batter, then whisk until smooth. Coat hot waffle grids with cooking-oil spray. Ladle 3/4 to 1 cup batter (or amount that waffle iron maker directs) onto hot iron and cook until nicely browned and crisp, 4 to 5 minutes. Transfer waffle directly to oven rack. Repeat with remaining batter. (If oven gets too full, remove plates.)
Meanwhile, in a small bowl, combine remaining 2 tbsp. sugar and the cinnamon.
Break waffles into sections and divide among the warm plates. Serve with bananas, maple syrup, cinnamon sugar, and yogurt if you like.
Note: Nutritional analysis is per serving.