Preheat oven to 325-F degrees and line two large baking sheets with aluminum foil. Pierce the sweet potatoes with a fork and place unpeeled potatoes on the baking sheets. Bake until very tender, usually about 1 1/2 hours. Let cool slightly.

Peel warm potatoes and place in a large mixing bowl. Beat or mash the cooked sweet potatoes until soft. Add the room-temperature butter, whipping cream, cardamom, and nutmeg. Whip until smooth and creamy. Season lightly with salt.

Transfer potatoes to a 9-inch by 13-inch baking dish. You may prepare the dish 1 day ahead of your meal. Cover and refrigerate. Bring the dish to room temperature before warming for the meal. Bake until the potatoes are heated through and beginning to brown on top, usually about 45 minutes in a 325-F degree oven. Serve warm.

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