Preheat the oven to 425 degrees F.
Cut the top 1/2-inch from each onion, peel the onions, and with a melon-ball cutter scoop out the centers, reserving the onion pieces, leaving 2 layers of onion or 1/3-inch-thick shells, leave the bottoms slightly thicker. Transfer the reserved onion pieces to a 13 by 9-inch glass baking dish. Drizzle the broth over them, and arrange the onion shells, inverted on top. Cover the dish tightly with foil and bake the onions in the middle of the oven for 45 to 50 minutes, or until the shells are just tender. Remove and reserve the shells. Into the onion pieces, stir the cream, the sugar, and salt and pepper, to taste, and bake the mixture, uncovered, stirring occasionally, for 25 minutes.
While the onions are baking, in each reserved onion shell layer 1/4 cup of the stuffing, 1 1/2 tablespoons cranberry sauce, and another 1/4 cup of the turkey. Holding each shell in one hand pack the layers lightly. Arrange the stuffed onions on top of the baked creamed onions and pour 2 tablespoons of the gravy into each stuffed onion. Top each stuffed onion with 1/3 cup of mashed potatoes, mound them, and score with a fork. Bake the onions, stirring the creamed onions occasionally, for 35 to 40 minutes, or until the potatoes are golden.