Preheat the oven to 350°.
Grease a 12 cup muffin tin and set aside.
In a medium-sized mixing bowl, mash your three bananas.
Mix in the brown sugar, and then add in the egg and vanilla.
Finally mix in all of the dry ingredients.
Scoop the muffin mixture into your prepared muffin tin, about ⅔ of the way full.
Using a small spoon, dollop a ½ tsp sized amount of Nutella on top. Swirl it in with a knife or toothpick.
Bake for 15-18 minutes, or until the middles bounce back.