The cooking time for a casserole depends largely on the cut of meat that is used. Nowadays, relatively tender cuts of meat are included, and these can be cooked successfully in as little as 1-2 hours.
In previous times, traditional casseroles were made with the tougher cuts from the leg, neck and shoulder of older animals. The well-developed muscle fiber and connective tissue could be broken down only by slow, moist cooking. Casserole meat is usually cut into pieces to accelerate this process.
These tough cuts of meat usually have an excellent flavor, with the connective tissue dissolving to a gelatine during slow cooking. This gives a very soft texture and an excellent rich, velvety sauce, but the process may take 3 hours.
** Asian Online Recipes