Preheat oven to 350°F.

Line your cupcake or muffin pan with cupcake liners. Mix flour, sugar, baking soda, and salt in a large bowl. Mix mashed bananas, egg, melted butter and milk in a separate medium bowl. Stir banana-milk mixture into dry ingredients just until blended with a rubber spatula (do not over-mix). Stir in chocolate chips and mix.

Divide batter into the lined cups, filling each about 3/4-almost full. Bake muffins until tops are pale golden and a toothpick inserted into the center comes out with some melted chocolate attached but clean of batter, (about 26-27 minutes or more depending on your oven). Transfer muffins out of the pan to cool completely. Store at room temperature in an air-tight container and eat within 3 days.