No need for a mixer for this recipe. Preheat oven to 350 F with a wooden spoon. Mix butter into the mashed banana in a large mixing bowl. Mix in the sugar, egg, and vanilla. Sprinkle the baking soda and salt over the mixture and mix. Add the flour last. Pour the mixture into a buttered 4X8 inch loaf pan. BAKE for one hour. Cool on a rack. Remove from pan and slice and serve.