Preheat the oven to 400℉. Line a regular-sized 12-count muffin tin with parchment paper liners or grease with non-stick spray or butter.

Cream together the butter and brown sugar in a large mixing bowl with a handheld mixer at high speed. Add the eggs, vanilla, and mashed bananas and continue mixing until incorporated.

In a separate bowl, whisk together the flour and baking soda. Add to the combined wet ingredients and continue mixing at low speed until just incorporated.

Fill each muffin liner half full with batter. Then, drop a teaspoonful of Nutella into each. Then add more batter to each liner to cover the Nutella and fill almost to the top. Add another teaspoonful of Nutella to the top and gently swirl around with a toothpick.

Bake the muffins in the 400℉ oven for 5 minutes before reducing the temperature to 350℉ for another 10-15 minutes or until a toothpick inserted into the muffin part comes out clean. Let cool in the pan for 10 minutes before transferring to a wire rack to finish cooling. Enjoy!