Oven-roasted sweet potatoes can turn out dry. The trick to achieving a soft outer skin with moist, tenderized flesh is to wrap the potato in foil and add a little water.
As the water heats up within the foil, it steam-bakes the sweet potatoes from within, keeping them hydrated as they cook.
Preheat your oven to 425 degrees Fahrenheit, wrap washed sweet potatoes in aluminum foil, pour about four to five tablespoons of water onto the foil, then seal it up tightly.
Place everything in the oven, and give them at least an hour before checking for doneness. Larger potatoes may take up to an hour and 25 minutes or more.
Another similar method uses a covered baking dish. Make a one-inch slit on the top of each sweet potato and place them into a dish filled with approximately ¼ inch of water.
Cover the dish with a lid or foil and bake at 400 degrees Fahrenheit until the sweet potatoes reach your desired softness.