Mash your bananas then add the sugar, eggs, and oil. Meantime, sift the dry ingredients together. Add the walnuts to the dry ingredients. Add the sour cream and dry ingredients to the banana mixture.

Grease with butter or vegetable oil shortening, and line with heatproof parchment paper three pieces loaf pans. Bake at 400 F for 15 minutes, then lower the temperature to 350F, and bake for another 20-30 minutes, or until the top exterior of the cake is almost firm to the touch.