This stuffing is an upscale riff on the popular sweet potato-marsmallow casserole.
Preheat oven to 400 degrees. Bake potatoes until tender, about 1 hour. Let cool; peel. Cut 1 potato into 1/2-inch cubes. Mash remaining 2 potatoes with butter.
Bring 4 cups water to a boil in a medium saucepan. Soak plums in 1 cup boiling water until plump, 5 to 7 minutes.
Dip persimmons in remaining water for 10 seconds each; rinse in cold water. Stem, peel, and core. Cut persimmons and plums into 1/4-inch-thick wedges.
Stir together fruit, sugar, zest, and cardamom. Scrape in vanilla seeds. Add salt and pepper. Stir in potatoes.
To bake stuffing: Cover with foil in an 8-inch square baking dish. Bake in a 350 degree oven 15 minutes. Remove foil; bake until heated through, about 5 minutes more. To cook in turkey: Immediately pack loosely in turkey cavity; cook until an instant-read thermometer inserted into center of stuffing registers 165 degrees.
