Heat oven to 350. Line a mini muffin pan with baking cups or lightly coat with cooking spray. In a medium-sized bowl, combine the flour, sugar, baking powder, and salt and stir with a fork to blend. In a mixing bowl, combine the mashed bananas, egg, melted butter, sour cream, vanilla extract, and milk. Beat on medium until well blended. Reduce speed to low and blend in the dry ingredients (do not over mix). Stir in the mini chocolate chips. Fill each muffin cup with about a tablespoon of batter. Bake the muffins for about 20 minutes or until tops are golden and a toothpick comes out with no crumbs. Transfer the muffins to a rack and cool. Makes about 36 mini muffins (or about 18 regular-sized muffins).