Preheat your oven to 350°F (175°C).
In a large bowl, mash the ripe bananas.
Stir in melted butter into the mashed bananas.
Mix in sugar, egg, and vanilla until well blended.
Sprinkle baking soda and salt over the mixture and mix in.
Stir in flour gently until just combined.
Fold in the chocolate chips.
Scoop the batter into a greased or lined muffin tin.
Bake for 18-20 minutes, or until golden brown.
Let cool in the tin for 5 minutes before transferring.