Scrub sweet potatoes and pierce in several places with a fork. Place potatoes on oven rack or in a single layer on a baking sheet. Bake in a 325° to 350° oven until potatoes give readily when gently squeezed, about 1 1/2 hours. Slit open; season to taste with gravy, butter, and salt and pepper.
Roast with the turkey; serve with gravy.