Preheat oven to 350 degrees. Coat muffin pans with non-stick spray or use paper liners. Sift together flour, baking powder, baking soda, and salt. Set aside.
In large bowl, combine bananas (mashed), sugar, egg, and butter (melted). Add flour mixture and beat until smooth. Scoop into muffin pans.
Bake for 10-15 minutes, or 20-25 minutes for large muffins. Tops will be brown and muffins will spring back when touched.