For the banana bread:

1. Preheat oven to 350 F. Line a loaf pan with parchment paper and spray with nonstick spray.
2. In a medium bowl, mash ripe bananas until smooth and slightly chunky.
3. In a large bowl combine melted or softened butter with brown sugar until smooth.
4. Add in eggs and whisk until smooth.
5. To the mixture, add milk and vanilla extract until combined. Add-in in the mashed bananas to the batter and mix until incorporated.
6. Add in flour, baking soda, and salt to batter and gently stir until batter is combined. Do not over mix, batter lumps are okay. 
   

For the cinnamon swirl: 

1. Mix together melted butter, brown sugar, and cinnamon and set aside. 

Pour 1/3 batter into a prepared loaf tin, smooth the top, and top with 1/3 of the cinnamon swirl mixture. With a butter knife or spatula, mix the cinnamon swirl into the batter lightly. Continue with two more increments and top with remaining cinnamon swirl mixture and 1 banana cut lengthwise.

Bake banana bread for 55-60 minutes or until a toothpick comes out clean. 

Allow banana bread to cool for 10-20 minutes before transferring to a wire rack and slicing.