Preheat your oven to 180°C (350°F) and line a muffin tin with paper cases.
In a large bowl, mash the bananas with a fork.
Add the sugar, egg, melted butter, and vanilla extract. Stir well.
Sprinkle in the baking soda and salt, mix again.
Gently fold in the flour until just combined.
Stir in the chocolate chips.
Spoon the batter into the muffin cases about 3/4 full.
Bake for 18–20 minutes, or until a toothpick comes out clean.
Cool on a wire rack and try not to eat them all at once.