Preheat oven to 350 degrees F (175 degrees C).
Coat muffin pans with non-stick spray, or use paper liners.
Sift together the flour, baking powder, baking soda, and salt; set aside.
Combine bananas, sugar, egg, vanilla and melted butter in a large bowl. Fold in flour mixture, and mix until dry ingredients are just combined. Do not over mix. Scoop about 1/4 cup of batter each muffin tin.
Bake in preheated oven for 15-20 minutes. Muffins will spring back when lightly tapped. My oven took about 3-5 minutes more, but start out with less time just to be safe.