Heat the oven to 350 degrees. Spray 4 (3x5-inch) baking pans with cooking spray.
In a large bowl, combine the sugar, sour cream, butter, eggs, and vanilla. Beat at medium speed until creamy. Fold in the mashed bananas.
Add the flour, baking powder, baking soda and salt. Beat at low speed only until moistened. Fold in the nuts. Spread the batter into the pans.
Bake for 40-45 minutes or until a toothpick inserted in the center comes out clean. Cool for 10 minutes in the pans and then remove from the pans to a cooling rack; cool completely.