Preheat oven to 350 degrees.
Spray and flour a mini loaf pan (makes 8 loaves). If you don't have a mini loaf pan, bake muffins in paper liners OR you may use a traditional size loaf pan - bread won't be quite as tender on the outside.
Cream butter and sugars, add eggs, bananas, buttermilk and vanilla and mix well.
Add dry ingredients and mix until smooth.
Divide into mini loaves and bake for 26-30 minutes, until tops are golden brown and split and bounce back when touched gently. (Cook 50-55 minutes for a large loaf)