Preheat your oven to 350°F (175°C). Grease a 12-cup muffin tin or line cups with paper liners.
In a bowl, sift together the flour, baking powder, baking soda, and salt. Set aside.
In a separate large bowl, mix together the mashed bananas, sugar, egg, and melted butter until well combined.
Fold the flour mixture into the banana mixture until smooth.
Spoon the batter into the prepared muffin cups, filling each about 2/3 full.
Bake in the preheated oven for 25 to 30 minutes or until the tops of the muffins spring back when lightly pressed.
Allow the muffins to cool briefly in the tin, then transfer them to a wire rack to cool completely.