Preheat the oven to 350°F (175°C). 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 last, mix. Fold in chocolate chips.
Pour mixture into a buttered 4x8 inch loaf pan or muffin tin. Bake for 1 hour for the loaf, or 22-25 minutes for the muffins. Cool on a rack. Remove from pan and slice to serve.