Preheat oven to 325°F. Butter or spray a 9×5 loaf pan.
In a bowl, sift flour, baking soda, cinnamon, and salt. Set aside.
Whisk sugar and eggs for 5–8 minutes until light and fluffy.
Slowly drizzle in oil on low speed, taking 1 minute.
Add mashed bananas, sour cream, and vanilla. Mix to combine.
Fold in dry ingredients and walnuts with a spatula.
Pour into loaf pan (don’t overfill). Bake 60–75 mins.
Tent with foil halfway to prevent over-browning.
Cool 30 mins in pan, then remove and finish cooling.
Slice and enjoy with butter or as-is.
