Preheat the oven to 350 F. Grease a muffin tin with cooking spray (or prep it with muffin liners).
In a large bowl and using a fork or whisk, mix the bananas, milk, butter, vanilla, egg, and sugar until well combined.
In another bowl, mix the flours, baking powder, baking soda, salt, and cinnamon together with a whisk or fork.
With a spatula, combine the wet and dry ingredients until just mixed (don't over mix! stop once the dry ingredients are mixed in with the wet). Fold in the chocolate chips and/or nuts if using.
Using a 1/4 cup measuring cup, add the batter to the muffin tin. Bake for 18-20 minutes, until the muffins are golden and firm to the touch. Let them cool completely before storing in an airtight container on the counter or in the fridge!