Preheat oven to 425°. Melt butter. Add sugar, baking powder, salt, bananas, egg, vanilla and milk in a large mixing bowl with a whisk. It's okay to leave chunks of banana in the batter. Add flour and 1 cup of chocolate chips. Stir gently with a wooden spoon just until combined. Don’t overmix the batter. Spray 13 muffin tins with cooking spray. Spoon batter evenly into each muffin tin. Sprinkle additional chocolate chips over top of batter. (I added close to 10 chocolate chips on top of each muffin). Bake at 425° for 5 minutes. Adjust temperature to 350°. Continue baking an additional 20 minutes or until a toothpick inserted in center comes out clean. Cool.