Preheat oven to 400ºF.  Butter 12 large muffin pans or line with paper muffin cups. Sift together flour, baking powder. Combine banana with brown sugar. Beat in eggs, milk and melted butter. Stir in dry ingredients only until blended. Stir in chocolate chips. Spoon into muffin cups. Bake 25 minutes until slightly brown. Cool on rack.