Make as many fruit stacks as desired, beginning with a pineapple slice, topping that with a peach half, an apricot half and a seeded whole prune. Stir together 1/2 cup melted butter, 1/4 cup dark brown sugar and 2 tablespoons dark rum. Spoon over fruit stacks and bake at 350 degrees F for 10 minutes. Baste with extra sauce and serve as an accompaniment to poultry or game. Sauce is sufficient for at least 8 fruit stacks.