Preheat your oven to 350°F (175°C). If using muffin liners, place them in the muffin tin.
In a mixing bowl, mash the ripe bananas with a fork until smooth.
Stir the melted butter into the mashed bananas.
Mix in the baking soda and salt.
Add the sugar, egg, and vanilla extract to the banana mixture. Stir until well combined.
Sprinkle the baking powder over the mixture and mix.
Gradually add the flour, stirring gently until just combined. Do not overmix; it’s okay if there are a few lumps.
Pour the batter evenly into the muffin tin, filling each liner or cup about two-thirds full.
Bake in the preheated oven for about 20 minutes, or until a toothpick inserted into the center comes out clean.
Let the muffins cool in the tin for a few minutes before transferring them to a cooling rack.