Preheat oven to 350.
Sift or whisk dry ingredients and set aside. Combine Herman and bananas; beating to break up bananas. Add egg, oil, zest, vanilla, and sugars and beat well. Stir in flour and spices; fold in optional ingredients if desired. Pour into well-greased 9" x 5" loaf pan. Bake for 1 hour. Cool in pan 10 minutes, loosen sides with knife or spatula, and turn out onto cooling rack. Makes 1 large loaf.
"Herman" is a milk-based New England sourdough that keeps this recipe nice and moist. Any sweet sourdough culture will work. If you don't have any, borrow a cup from a neighbor - that Friendship Cake recipe is always going around, complete with little bags of the sourdough culture. Feed Herman with 2 parts flour, 2 parts milk, and 1 part sugar. He will keep for a week, covered, on your counter and nearly indefinitely in your fridge.