1. Preheat oven and wash the sweet potatoes: Preheat oven to 375°F. Scrub the sweet potatoes well and pat them dry with a dish towel. 2. Oil them up: Prepare squares of aluminum foil for as many sweet potatoes as you are roasting. Place each potato on a foil square and drizzle with a small amount of vegetable oil. Using your hands, rub the oil in a thin, even layer all over the potatoes. 3. Prick with a fork, wrap, and roast: Prick each sweet potato several times with a fork and wrap loosely in the foil. Be sure the foil is well-sealed.