Preheat the oven to 325 F. Rinse the roast and pat dry with paper towels.
In a bowl, combine the mustard, sea salt, pepper, rosemary and garlic. Rub the mixture over the roast.
Place roast, fat side up, in a roasting pan and cook for about 2 to 2 ½ hours, or until internal temperature reaches 150 F. Once removed from the oven, let rest for 15-20 minutes. Slice and serve.