Preheat your oven to 350°F (175°C) and line a muffin tin with paper liners or grease lightly.
In a large bowl, mash the bananas with a fork until smooth.
Stir in melted butter, sugar, and brown sugar. Mix in the egg and vanilla.
Sprinkle the flour, baking soda, and salt over the wet mixture and stir until just combined—don’t overmix!
Fold in the chocolate chips gently.
Scoop the batter evenly into the muffin tin—aim for about 3/4 full each.
Bake for 18–22 minutes, or until a toothpick poked in the center comes out clean.
Cool in the pan for 5 minutes, then transfer to a wire rack (if you can wait that long before digging in).