Cream butter and sugar.
Add eggs, one at a time, and mix until light and fluffy.
Add flour, baking soda, and salt and mix until combined.
Add vanilla, sour cream, and mashed bananas.
Fold in chopped walnuts.
Bake in greased loaf pan at 350 degrees. For a regular loaf pan, bake 55-60 minutes. For a mini loaf pan (makes 2), bake 30-35 minutes. For muffins, bake 20-25 min.