Preheat oven to lowest possible temperature setting, 150°F (66°C) or higher if necessary. (Some ovens cannot hold a temperature below 250°F/121°C.) Season roast generously with salt and pepper. Place roast, with fat cap up, on a V-rack set in a large roasting pan, or on a wire rack set in a rimmed baking sheet. Place in oven and cook until center of roast registers 120-125°F (49-52°C) on an instant-read thermometer for rare, 130°F (54°C) for medium-rare, or 135°F (57°C) for medium to medium-well. In a 150°F oven, this will take around 5 1/2 to 6 1/2 hours; in a 250°F oven, this will take 3 1/2 to 4 hours.
Remove roast from oven and tent loosely with aluminum foil. Place in a warm spot in the kitchen and allow to rest for at least 30 minutes and up to 1 1/2 hours. Meanwhile, preheat oven to highest possible temperature setting, 500 to 550°F (260 to 288°C).
Ten minutes before guests are ready to be served, remove foil, place roast back in hot oven, and cook until well browned and crisp on the exterior, 6 to 10 minutes. Remove from oven, carve, and serve immediately.