Preheat your oven to 350 degrees. Spray a 9 by 5 inch loaf pan with cooking spray.
In a large bowl whisk together the flour, baking soda, and salt.
In a smaller bowl whisk together the bananas, cooled butter, eggs, sour cream, sugar, and vanilla.
Gently fould the wet ingredients into the dry ingredients. Stir until they are just combined.
Pour half the batter into the preapred baking pan. Spoon half the softened Nutella onto the top of the batter in three different scoops. Using a butter knife, swirl the Nutella into the batter. Repeat with the remaining batter and the remaining Nutella.
Bake for 55 to 65 minutes or until a toothpick inserted into the middle of the bread pan comes out clean.
Let the bread cool in the bread pan for 10 minutes before removing it and transferring it to a wire cooling rack. Cool completely (about an hour) before slicing. Enjoy or store in an airtight container for three to four days. See instructions in the post for freezing.