Line a 12 count muffin with paper liners. Or grease each muffin cup.
In a bowl, add flour, baking powder, baking soda, and salt in a bowl. Whisk together and set aside.
In another bowl, whisk the bananas, sugar, egg, vanilla together. Then drizzle in the melted butter while whisking.
Add the flour mixture to the wet mixture and fold together. Mix until dry ingredients are just combined. Do not over mix.
Bake at 350 degrees oven for 15-20 minutes. Muffins will spring back when lightly tapped and a toothpick insterted in the center comes out clean. Makes 12 muffins.