Prime Rib Perfection

In a small bowl, combine 1/4 cup mustard, rosemary, garlic, 1 teaspoon salt and 1 teaspoon black pepper.  Rub mixture over entire surface of meat.

Roast, fat-side-up in a large roasting pan 15 minutes.  Reduce heat to 325 degrees. For medium-rare doneness, cook 2-1/4 to 2-1/4 hours, or until internal temperature reaches 135 degrees.  For medium doneness, cook for 2-3/4 to 3 hours, or until internal temperature reaches 150 degrees.

Remove from oven and transfer meat to cutting board.  Tent with foil and allow to rest 15 to 20 minutes.  Temperature of meat will continue to rise 5 to 10 degrees to reach desired doneness.

Meanwhile, stir sour cream, horseradish, 1 tablespoon mustard, 1/2 teaspoon salt, 1/4 teaspoon black pepper and half-and-half in a bowl.  Serve on prime rib slices.