Preheat your oven to 350°F (175°C).
In a mixing bowl, mash the ripe bananas with a fork.
Add the melted butter to the mashed bananas and mix well.
Stir in the sugar, beaten egg, and vanilla extract.
Sprinkle the baking soda, baking powder, and salt over the mixture and mix in.
Add the flour last, and mix until just combined.
Pour the batter into a prepared muffin tin.
Bake for 20 minutes, or until a toothpick inserted into the center comes out clean.
Let the muffins cool in the tin for a few minutes, then transfer to a wire rack to cool completely.