At least 1 hour before grilling, soak wood chips in enough water to cover (drain wood chips before using).
Trim fat from meat.
Grill over medium to low indirect heat. Sprinkle half of wood chips over the coals. Place meat on the smoker rack.
Add remaining wood chips halfway through grilling. Remove meat from grill, cover with foil and let stand for 15 minutes.
Cover and grill until done. Allow 1 3/4 to 2 1/4 hours for medium rare and 2 1/4 to 2 3/4 hours for medium.
The temperature of the meat after standing should be 145°F for medium rare, and 160°F for medium.
Meanwhile, in a small mixing bowl, beat whipping cream with a rotary beater or wire whisk until slightly thickened and starts to mound. Stir in mustard and rosemary.
Serve immediately over lamb slices. If desired, sprinkle with pepper.