No need for a mixer for this recipe. Preheat the oven to 350°F. With a wooden spoon, mix butter into the mashed bananas in a large mixing bowl. Mix in the sugar, egg, and vanilla. Sprinkle the baking soda and salt over the mixture and mix in. Add the flour and mix. Stir in chocolate chips. Pour mixture into a buttered 5 x 9 loaf pan. Bake for 45-57 minutes. Cool on a rack. Remove from pan and slice to serve.