Preheat the oven to 350°F (175°C).

In a large mixing bowl, mash the ripe bananas.

Add the melted butter to the mashed bananas and mix well.

Mix in the sugar, egg, and vanilla extract.

Add the baking soda and salt, then mix thoroughly.

Gradually add the all-purpose flour and mix until just combined.

Grease a muffin tin with vegetable oil.

Pour the banana bread mixture into the prepared muffin tin, filling each cup about 2/3 full.

Bake for 25 to 35 minutes, or until the muffins are golden brown and 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 wire rack to cool completely.