For lamb stew that's succulent and fall-apart tender you need to start with the right cut and cook it right, sunshine842 says on Chowhound. While cubed meat from the leg will make a respectable stew, lamb shoulder is a far better choice: It has plenty of fat and connective tissue, which impart flavor and a silky texture after long cooking. Avoid mystery lamb labeled "stew meat." Without knowing what cut (or cuts) the meat's from, you can't judge how long you'll need to simmer it to make it tender, hankstramm says.
The key to cooking any tough cut is slow simmering over low heat—lamb shoulder could take upward of two hours to reach the tender zone. Don't be alarmed if the meat seems quite tough after it's cooked for a while, sunshine842 says. The muscle fibers seize up, then relax into a state of tenderness after more cooking. Just keep simmering.
Note that an acidic marinade can tenderize the meat and reduce cooking time. Try olive oil and red wine vinegar for a Mediterranean stew, or yogurt mixed with spices for an Indian curry.
Discuss: How to cook lamb properly?
Photo of CHOW's Tunisian Lamb and Quince Stew by Chris Rochelle / CHOW.com