Preheat oven to 350°.
Beat butter, sugar, vanilla, and, egg until combined. Set aside.
With a potato masher or a fork, mash in banana.
Add the mashed bananas with butter, sugar, and egg mixture and fully mix until combined.
Add flour, baking soda, and salt.
Stir until everything is mixed.
Fold in the nuts.
Spray a loaf pan with non-stick cooking spray.
Pour mixture into loaf pan.
Cook for 55-65 minutes or until an inserted toothpick comes out clean.
Cool for 1 hour before removing from the baking pan.