Mix together the egg, sugar, & vegetable oil until combined. Add the flour mixture and blend. Add buttermilk, vanilla, and mashed bananas. Mix until combined.
5 Fold in 1/2 cup chopped walnuts and pour batter into prepared loaf pan.
6 Top batter with remaining 1/3 cup chopped walnuts.
7 Bake for 45-60 minutes, until a toothpick inserted in the center comes out clean.
8 Cool for 10 minutes on a wire rack before removing from pan.