Prepare a slow charcoal fire with hardwood charcoal. Soak 1 1/2 lbs of wood chips (hickory, cherry or other hardwood or fruitwood) in water for 20 minutes. When coals are glowing and coated with white ash, spread evenly and top with wood chips. Place lamb on a rack in grill. Cover and smoke 2 1/2 hours, turning every half hour and checking to make sure there are no flames -- if flaming, douse with a little water. Cool. Refrigerate lamb overnight. Slice lamb from bone, and shred slices. The meat will still be mostly raw.
Prepare Barbecue Sauce: In a large pot combine molasses, tomato puree, chili sauce, mustard, Worcestershire, Tabasco and garlic. Add lamb and simmer for one hour.
Meanwhile, prepare Mint Butter: In workbowl of food processor combine mint and shallots and pulse to puree. Add butter and process until completely incorporated.
When lamb is ready, remove from heat and stir in mint butter. Serve