Preheat your oven to 350°F (175°C) and line a muffin tin with cupcake liners.
In a mixing bowl, whisk together the flour, baking powder, baking soda, and salt.
In another bowl, mix the mashed bananas, sugar, melted butter, vanilla extract, and egg until well combined.
Gradually add the dry ingredients to the wet ingredients, mixing until just combined.
Divide the batter evenly among the cupcake liners, filling each about ⅔ full.
Bake for 18-20 minutes, or until a toothpick inserted into the center comes out clean.
Let the cupcakes cool in the tin for 5 minutes, then transfer to a wire rack to cool completely.