Preheat oven to 400 degrees. In a large bowl, combine bananas, egg, oil and milk. Mix well. Add flour, brown sugar and baking powder, stirring just until moistened. Set aside 1/4 c. of the toffee bits; stir remaining toffee bits into the batter.
Lightly grease 18 muffin cups, or line them with paper baking cups. Fill cups 2/3 full with batter. Sprinkle with reserved toffee bits and bake for 18-20 minutes, or until a wooden toothpick inserted in the center of the muffin comes out clean. Cool for 5 minutes in the pan on a wire rack. Remove muffins and cool completely on the wire rack.