Preheat oven to 350°F (175°C) and line a muffin tin with paper liners.

In a mixing bowl, mash ripe bananas until smooth.

Stir in melted butter, sugar, egg, and vanilla until well combined.

In another bowl, whisk together flour, baking powder, and salt; gradually fold into banana mixture until just combined.

Fill muffin tins about two-thirds full and bake for 18-20 minutes or until golden brown.

Cool for five minutes before transferring to a wire rack.