Preheat the oven to 350°F.
Prepare a loaf pan by lining it with parchment paper or greasing it.
Mix together in a medium sized bowl the flour, baking soda, baking powder, salt and walnuts. Set the bowl aside.
1 ½ cups flour, ¾ teaspoon baking soda, ¾ teaspoon baking powder, ¼ teaspoon salt, ¼ cup chopped walnuts
In another bowl, cream together the butter and sugar until smooth and creamy. Then mix in the egg. Add in the buttermilk, vanilla, and mashed bananas.
¾ cup sugar, ¼ cup salted butter, ½ cup buttermilk, ½ teaspoon vanilla, 3 large mashed bananas, 1 large egg
Add the dry ingredients to the wet ingredients and mix until just combined.
Bake at 350°F for 60 minutes or until a toothpick or cake tester inserted in the center comes out clean.
Cool on a wire rack for 10 minutes before removing banana bread from the pan.