Cream brown sugar and 1 cup butter, add eggs 1 at a time; beat well. Add mashed bananas and flour and salt, baking soda along with 1 cup sour cream . Add vanilla and nuts last.
Pour batter into 3 - 9 inch pans or a 13 x 9 inch pan. Bake in a preheated 350 degrees F (175 degrees C) oven until cake tests done with a tooth pick, about 30 to 40 minutes for the 9 inch round cakes or about 40 to 50 minutes for the 13 x 9 inch cake..
To make Frosting: Mix 1/2 cup of butter or margarine, 4 cups of confectioners' sugar and 1/4 cup sour cream (more if needed). Add 1 teaspoon vanilla and beat until fluffy.