Scrub medium baking potatoes (or yams or sweet potatoes). Brush with salad oil. Wrap each in a piece of foil, overlapping ends. Bake 45 to 60 minutes on the grill or right on top of coals. Turn occasionally. Pinch to tell when done. Cut crisscross with fork in top of package, push on ends to fluff, and add a chunk of butter. Season