Position an oven rack in the lower third of the oven and preheat the oven to 275°F.
Put the roast on a roasting rack in a roasting pan. Hold a blowtorch about 1 inch from the roast and turn to lightly brown the fat on all sides; the idea is to start the fat rendering and to torch the meat just until the surface begins to turn gray. Season the roast generously with salt and pepper.
Transfer to the oven, with the meat toward the back of the oven, and cook until the roast registers 128°F in the center. The total cooking time will be about 2 hours, but begin to check the temperature after 1½ hours. Remove from the oven and let rest in a warm spot for at least 30 minutes for medium-rare.
To carve, cut the meat away from the bones. Separate the bones and put them on a serving platter. Cut the roast in half through the center, turn each piece cut side down, and slice straight down into slices that are about ½ inch thick. Arrange the meat on the platter and sprinkle with gray salt and pepper.
Serve with the horseradish cream on the side.