Preheat oven to 350°F. Lightly grease and flour a 9×5-inch loaf pan and set aside.

In a large bowl, melt the butter and let cool slightly. Whisk in the sugar then the eggs and vanilla. Stir in the flour and baking soda. Fold in the mashed bananas until just combined.

Spread ¼ of the bread batter evenly into the bottom of the prepared pan. Dollop ¼ cup of Nutella over the batter in the pan and then make a nice thick swirl through the batter with a table knife or bottom of a wooden spoon. Place ⅓ of the remaining batter evenly over the first layer and swirl with ¼ cup of the remaining Nutella. Place ½ of the remaining batter evenly over the second layer and swirl with ¼ cup of the remaining Nutella. Spread the remaining batter evenly over the top and dollop with the remaining ¼ cup Nutella. Make large swirls throughout the entire loaf.

If desired, slice half of a banana into little chunks and place them over the swirled batter.

Place the loaf pan on a baking sheet and bake for 60-70 minutes or until golden brown and a toothpick inserted in the center comes out clean. If the top of the loaf looks baked before the inside is completely baked, tint the loaf with foil and let continue baking until baked all the way through.

Let the bread cool in the pan for at least 30 minutes before removing to a wire rack to cool.