Preheat oven to 350 degrees. Line twelve 1/3-cup muffin cups with foil muffin liners.
Mix flour, sugar, baking powder and salt in large bowl. Mix mashed bananas, egg, melted butter and milk in medium bowl. Stir banana mixture into dry ingredients just until blended (do not overmix). Stir in chocolate chips.
Divide batter among prepared muffin cups, filling each about 3/4 full. Bake muffins until tops are pale golden and tester inserted into center comes out with some melted chocolate attached but no crumbs, about 32 minutes. Transfer muffins to rack; cool.
This recipe yields 12 muffins.