Preheat oven to 300°F (150°C). Grease two 7×3 inch loaf pans or line with parchment paper.
In a large bowl, cream butter and sugar. Mix in eggs, mashed bananas, sour cream, vanilla and cinnamon. Mix in salt, baking soda, and flour. Divide into prepared pans. Drop 5 tablespoons of nutella, on top of each loaf, spacing it evenly across top. Then using a knife, swirl the nutella into the batter a few times. Careful not to swirl too much.
Bake for 1 hour, until a toothpick inserted in center comes out clean.
The nutrition information provided are only estimates based on an online nutritional calculator. This is not a comprehensive list of all the nutrients in the recipe (i.e., does not include vitamins, cholesterol, etc). I am not a certified nutritionist. Please consult a nutritionist or doctor for accurate information and any dietary restrictions and concerns you may have.