Preheat oven to 325°F. Grease one loaf pan and coat with flour. Mix: flour, baking soda, and salt together to make flour mixture. Mix: egg, sugar, and vegetable oil then add flour mixture and mix. Mix in buttermilk, vanilla extract, and bananas. Mix in 1/2 cup walnuts.
Pour batter into pan. Top with 1/2 cup walnuts.
Bake for 45-60 minutes, until a toothpick can cleanly be removed. Let cool 10 minutes on metal rack before removing from pan.