2. Use a paring knife to make 40 slits all over the lamb. Place a Roasted Garlic Slice in each slit.
3. Combine rosemary, mustard, olive oil, salt and pepper in a mixing bowl. Rub the mixture on lamb.
4. Roast uncovered in oven for about 1 hour. Begin to check temperature and continue roasting until the thickest parts reach 135°F for medium rare. Check every 10 minutes until the roast reaches desired doneness.
5. Rest the lamb for 10-20 minutes before carving.