Pre-heat oven to 350.
Brown the butter by adding to a saucepan over medium-low heat & stir to avoid burning. This process takes 5-10 minutes.
Allow the butter to cool for 5 minutes then beat in a stand mixer with brown sugar for 2 minutes.
Once fully combined, add in three mashed bananas.
Mix again.
Then add in the egg, milk, & vanilla extract.
In a separate bowl, whisk together flour, & baking powder. Then fold into the wet batter.
In a separate bowl, mix together the cinnamon & sugar.
Scoop half of the banana muffin batter into a lined muffin pan. You want to only fill up the muffin cup
1/3 to 1/2 the way to the top
Sprinkle on cinnamon sugar then top with the remaining batter then top with remaining cinnamon sugar. This will make 4 layers to the muffin.
Bake for 25-30 minutes.
