Rub roast with salt and pepper; dust with crushed gingersnaps. Place roast, fat side up, in a shallow roasting pan. Insert meat thermometer, being careful not to touch bone or fat.
Bake roast at 350° for 1 hour. Place sweet potatoes around roast; continue baking an additional 1 1/2 hours or until meat thermometer registers 170°.
Transfer roast to a serving platter. Let stand 10 to 15 minutes before slicing. Split sweet potatoes, and serve with butter.