Preheat oven to 375 degrees. Grease muffin tin.
Peel and mash bananas and set aside. You still want to leave some chunks in the mashed bananas.
In a large bowl, mix together flour, baking soda, baking powder, and salt.
In another bowl, combine the mashed bananas, white sugar, egg, vanilla, cinnamon, nutmeg and melted butter.
Pour the contents of the banana bowl into the large bowl with the flour mixture. Stir to combine, but don't over stir.
Scoop batter into muffins tins. This recipes makes 14 muffins so you can evenly divide the batter among 14 muffin cups.
To make the topping for these banana crumb muffins, you will mix together ⅓ cup of brown sugar, 3 tablespoons of flour and ¼ teaspoon of cinnamon. Using a fork or pastry cutter, cut in 2 tablespoons of butter until the mixture becomes crumbly.
Evenly sprinkle the crumb topping over the batter in the muffin tin.
Bake at 375 degrees for 18-20 minutes. To check for doneness, insert a toothpick into the center of the muffin. If it comes out clean, the muffins are ready to be enjoyed.
Remove muffins from oven and allow to cool on a cooling rack.