Poke potatoes all over with a fork. Place in single layer in microwave. Microwave for 5 minutes on High. Turn potatoes over and cook an additional minute at a time until softened, if necessary. When potatoes are cool enough to handle, cut off the top 1/3 of the potato. Scoop out flesh into a large mixing bowl, leaving a 1/4-inch a shell. Place shells on a baking sheet and set aside. Add butter, half and half, brown sugar, pumpkin pie spice and salt to sweet potato pulp. Whip potatoes until creamy, using a potato masher or electric mixer. Stir in dried cranberries. Spoon mixture back into skins. Cover and refrigerate at this point until 30 minutes before serving time. Meanwhile, children can decorate white paper sails. Cut 2 slits for toothpick mast near the bottom center of each sail. Thread toothpick through slits in sail. Set aside. Preheat oven to 350ºF. Arrange marshmallows over top of potatoes. Bake potatoes, uncovered, for 10 to 15 minutes or until marshmallows are golden brown and potatoes are hot. Place potatoes on serving platter and insert a sail into each potato. Makes 6 servings.