Break string-beans into pieces and let boil in salted water until tender; then heat 1 tablespoonful of butter; stir in 1 tablespoonful of flour until brown. Add the water in which the beans were cooked, ½ cup of vinegar, 1 tablespoonful of brown sugar, some cinnamon and cloves to taste. Let sauce boil. Add the beans and simmer ten minutes. Serve hot with a beef pot roast.