Preheat the oven to 350ºF.
Mix butter into the mashed bananas.
Mix in sugar, egg, and vanilla.
Sprinkle the baking soda and salt over the mixture and mix in.
Add the flour last, mix.
Pour mixture into a buttered 4x8 inch loaf pan.
Bake for 1 hour.
Add some chocolate chips and walnuts, if you like.