Preheat oven to 350°F. Grease a standard loaf pan and set aside.
Mash bananas and set aside.
In a large bowl, combine flour, baking soda, and salt and whisk together. Set aside.
In a stand mixer or large mixing bowl combine butter and sugars and beat together until creamy.
Add eggs one at a time and whip until light and fluffy.
Add sour cream, milk, and vanilla. Mix until incorporated, scraping down the sides of the bowl.
Add in bananas, mix together and scrape down sides of the bowl.
Add in dry ingredients ½ cup at a time. Mix until just incorporated. Continue until all ingredients are combined.
Pour half of the batter into the prepared loaf pan. Warm Nutella until pliable. Dollop half of the Nutella on top of the batter. Using a knife, swirl the Nutella into the batter.
Add the remaining half of the batter and top with the remaining Nutella. Swirl the Nutella and banana bread batter together.
Bake at 350°F for 55 minutes. Test every 5 minutes with a toothpick until it comes out mostly clean.
Allow to cool for about 15 minutes and remove from the pan. Transfer to a wire rack to allow to cool completely. Slice and serve.
