Pat lamb dry. In small bowl, combine mustard, 2 cloves garlic, 1/2 tsp/2 mL pepper and 1 tbsp/15mL rosemary. Spread over lamb. Allow to marinate while preparing potatoes. Arrange potatoes, onions and remaining garlic in bottom of roasting pan. Sprinkle with remaining rosemary, pepper and salt. Pour wine over top. Place lamb on top of potatoes. Roast in preheated 400F/200C oven for 80 to 90 minutes for rare. Meat thermometer should read 130F/55C. Turn roast once during cooking. Allow roast to rest 10 minutes before carving. Serve with potatoes and onions. NOTES : The potatoes in this dish absorb all the delicious lamb juices. Use any leftover lamb in a grilled meat salad. Recipe from Simply HeartSmart Cooking With Bonnie Stern. Makes 10 to 12 servings.