Preheat your oven to 350°F (175°C).
Cream together the softened butter and white sugar until light and fluffy.
Add the eggs one at a time, mixing well after each addition. Fold in the mashed bananas.
Pour in the sour cream and vanilla extract, stirring until smooth.
In a separate bowl, whisk together the flour, cinnamon, baking soda, and salt. Gradually add to the wet ingredients, stirring gently.
Fold in the chopped walnuts.
Grease your loaf pan and pour in the batter, smoothing the top.
Bake for 60 to 70 minutes, or until a toothpick comes out clean.
Let cool in the pan for 10 minutes, then transfer to a wire rack to cool completely before slicing.
