Wash the prunes, cover with water and cook until tender. Remove pits. Wash the raisins and drain. Cover with hot water and let stand until soft and plump.
Simmer sago (or tapioca) slowly in the 2 quarts of water with the cinnamon stick until soft, about 1 hour.
Add the prunes, raisins and juice. Taste, and add whatever amount of sugar suits your palate. Simmer slowly for 1 hour more.
If you have white wine in the house, add ½ cup and bland while the soup is warm. Top with whipped cream if you wish.
Serve at once.