Preheat the oven to 325℉. Line muffin tins 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 on high speed. Add the eggs, vanilla, and mashed bananas and continue mixing until fluffy.
Next, add the flour and baking soda and continue mixing on low speed until just incorporated.
Fill each muffin liner half full with batter. Then, drop a measuring teaspoonful of Nutella into each. Then add another spoonful of batter to each liner to cover the Nutella. Bake the muffins one pan at a time in the preheated oven for 20-24 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. Bake the remaining muffins. Enjoy!
Notes
Store cooled muffins in an airtight container at room temperature for up to 5 days.