Pierce sweet potatoes, and place on a baking sheet. Bake in a preheated 425 degrees F (220 degrees C) for 1 hour, or until tender. Cool until sweet potatoes can be easily handled. Peel, and cut into 1/4 inch thick slices.
In a small bowl, combine honey, cinnamon, salt, lemon and prune juice, and melted margarine.
Cut prunes in half, and remove pits. In a casserole dish, arrange alternating layers of potatoes and prunes. Spoon honey mixture over each layer.
Bake at 350 degrees F (175 degrees C) for 45 minutes, basting occasionally with liquid in casserole dish.