Preheat your oven to 350°F. Spray a 9x5 loaf pan with nonstick spray and line it with a piece of parchment paper.
In a large bowl, combine the butter, bananas, brown sugar, sugar, eggs, and vanilla. Mix well until combined.
1/2 cup salted butter, 3-4 ripe bananas, 1/2 cup (100g) brown sugar, 1/4 cup (50g) granulated sugar, 2 large eggs, 1 teaspoon pure vanilla extract
Add the flour, baking soda, baking powder, and salt. Stir until just combined.
1 3/4 cups (247g) all-purpose flour, 1 teaspoon baking soda, 1 teaspoon baking powder, 1/2 teaspoon salt
Place the Nutella in a small microwave-safe bowl and warm for 30 seconds until thinned.
1/2 cup Nutella
Pour half the batter into the pan. Spoon half the Nutella over the batter and swirl them together with a knife. Add the remaining batter to the pan, spoon the remaining Nutella over the top, and swirl them together with a knife.
Bake for 60-70 minutes until a toothpick is inserted in the center of the loaf and it comes out clean.
Allow the bread to cool for 15 minutes before slicing.