Rack of lamb is best eaten rare to medium. Remember that it should rest a bit before carving; this means there will be some carryover cooking after the rack is removed from the oven: the internal temperature will rise 5 to 10 degrees F. Be sure to remove the roast from the oven at 5 degrees F or so lower than the required doneness to compensate. For best results, always use an instant-read thermometer.