Preheat the oven to 350℉. Prepare your muffin pan by spraying with oil or using muffin liners.
In a large bowl or a stand mixer, beat on medium speed the bananas, melted butter, maple syrup, egg, vanilla extract, and milk.
In a separate small bowl, whisk together the flour, baking powder, baking soda, salt and cinnamon. Pour the dry ingredients into the wet ingredients, then beat or whisk until combined.
If adding nuts or chocolate chips, fold them in now. The batter will be thick.
Fill the pans with batter, filling them all the way to the top. Bake for 22-25 minutes or until a toothpick inserted in the center comes out clean. For mini muffins, bake for 12–14 minutes.
