1. Heat the oven to 350° F.
2. Line a mini muffin pan (ours made muffins 1 3/4 inches in diameter) with bake cups or lightly coat the muffin cups with cooking spray.
3. In a medium-size bowl, combine the flour, sugar, baking powder, and salt and stir with a fork to blend.
4. In a mixing bowl, combine the mashed bananas, egg, melted butter, sour cream, vanilla extract, and milk. Beat on medium until well blended. Reduce the speed to low and blend in the dry ingredients (do not overmix). Stir in the mini chocolate chips.
5. Fill each muffin cup with 1 level tablespoon of batter. Bake the muffins for about 20 minutes or until the tops are golden and a toothpick comes out with some melted chocolate but no crumbs.
6. Transfer the muffins to a rack to cool. Repeat with the remaining batter. Makes 36 mini muffins.