1. In a large bowl, stir together flour, sugar, baking powder, baking soda, cinnamon, nutmeg, and salt. In another bowl, mix egg yolks, milk, banana, sour cream, and butter until well blended. Stir egg-yolk mixture into flour mixture just until combined. Stir in pecans.
2. In another large bowl, with an electric mixer on high speed, beat egg whites until soft peaks form. Gently fold into batter until no white streaks remain.
3. Turn a Belgian waffle iron to high heat; brush both sides lightly with oil or melted butter. When hot, add about 1/2 cup batter per 4-inch square; close iron and cook until waffle is well browned (lift lid slightly to check), 6 to 9 minutes. Remove waffle; keep warm on a baking sheet in a 200° oven up to 15 minutes. Repeat to cook remaining waffles.
4. Serve warm with chunky pineapple sauce, maple syrup, and additional sliced bananas, if desired.
Chunky pineapple sauce: In a 1- to 2-quart pan over medium heat, stir 1 1/2 cups fresh pineapple chunks and 3/4 cup sugar until sugar is dissolved and juices are bubbling, about 5 minutes. Let cool 5 minutes, then whirl in a blender until smooth. Stir in 1 cup finely chopped fresh pineapple and 1 tablespoon lemon juice. Makes 2 cups.
Note: Nutritional analysis is per waffle.