Cover the casserole dish and place it in the oven for 4 hours at 130°C (this is an approximate cooking time for 2 kg of meat; it may need to be increased depending on the weight of your leg of lamb).
Halfway through cooking, remove the casserole dish and turn the lamb over so that it absorbs the broth evenly on all sides.
To check if your slow-cooked leg of lamb is tender, perform a tenderness test: pierce the meat with a fork; if it goes in without resistance and comes out easily, the lamb is cooked through. If not, extend the cooking time by half an hour and repeat the test.