Preheat the oven to 350 degrees. Grease and flour one 9-inch loaf pan or several smaller pans.
In a large bowl, cream the butter with the sugar until light and fluffy. Add the eggs and mix well. Whisk together the flour, baking soda, and salt; combine with the butter mixture. Add the bananas, sour cream, and vanilla; stir well. Fold in the nuts. Pour into the prepared pan and bake for 1 hour, or until a wooden pick inserted near the center of the loaf comes out clean. Cool in the pan for 10 minutes, then turn out onto a rack.
Makes one loaf.