Preheat oven to 350 degrees. Spray a loaf pan with cooking spray and set aside.
In a large bowl, whisk together the bread flour, sugar, baking soda and salt.
In a medium bowl, whisk together the butter, egg and buttermilk.
Add the wet mixture to the dry ingredients and whisk to combine. Fold in the mashed bananas and butterscotch sauce.
Transfer the batter to the prepared loaf pan. Bake for 50 to 55 minutes or until a toothpick inserted in the center comes out clean.
Cool on a wire rack for 10 minutes then remove loaf from the pan and let cool completely.