1. Preheat oven to 325 degrees.
2. Grease three 9 x 5 loaf pans.
3. In a large mixing bowl,mix butter and sugar together until well combined.
4. Add eggs, mashed bananas,sour cream, and vanilla.
5. Sift together flour and cinnamon and slowly add to batter. Mix until well combined.
6. Fold in walnut if using.
7. Pour batter evenly into prepared pans.
8. Bake 1 hour or until inserted tookpick comes out clean.
9. Serve warm or cool completely on wire rack