Oven method: Preheat oven to 400°F. Prick potatoes a few times with a fork. Place on baking sheet and bake 50 to 60 minutes, or until soft when pierced by a fork. Allow to cool slightly before serving, 5 to 10 minutes. Split potatoes open and sprinkle with ground cinnamon, nutmeg, cloves, ginger, or allspice. Microwave method: Prick potatoes twice with a fork. Place side by side on a paper towel in center of microwave oven. Cook on high 5 to 8 minutes, or until soft when pierced by a fork. Sprinkle with ground cinnamon, nutmeg, cloves, ginger, or allspice. Note: The skin of sweet potatoes contains many nutrients and fiber and should be left on and eaten whenever possible.