Preheat the oven to 350°F. Place 18 cupcake liners into your cupcake/muffin pan.
In a medium mixing bowl, whisk together 2 cups all purpose flour, 1 teaspoon baking soda, ½ teaspoon baking powder and ½ teaspoon salt then set it aside.
In the bowl of a stand mixer (or a bowl and an electric hand mixer), combine ½ cup (1 stick) unsalted butter, melted, 6 ripe bananas, mashed, ½ cup light brown sugar, packed, ¼ cup granulated sugar, 2 large eggs and 1 teaspoon vanilla extract. Beat at medium speed for 3 minutes.
Gently stir the flour mixture in until just combined. Set aside.
Place 1/3 cup Nutella in a small microwave-safe bowl and warm for 30 seconds until it's thinned.
Fill the cupcake liners so they are ¾ full with the muffin mixture.
Spoon the warmed Nutella over the batter, and swirl them together with a knife.
Bake for 15-18 minutes until a toothpick is inserted in the center of the muffins and comes out clean.
Move the muffins over to a cooling rack and allow them to cool for 15 minutes. Then enjoy!
Notes
Please refer to my FAQ’s (Frequently Asked Questions) and ingredient list above for other substitutions or for the answers to the most common questions.