Pre-heat oven to 120C (100C fan-forced)Using a small, sharp knife, pierce lamb twelve times; push garlic into slits, season. Place lamb in a large oven bag in a large baking dish. Combine tomatoes and stock in a bowl, season, pour into bag over lamb. Tie to secure.Roast lamb 8 hours. Remove from oven; rest 10 minutes before slicing. (didn't need to slice, it melted apart)Combine sour cream and lemon, serve with the lamb and parmesan.