Wash and dry the lamb. Rub in salt and pepper to taste. Choose a saucepan just big enough to hold the meat and melt all the butter in it. Add the lamb and gently simmer for 24 hours for that rich taste.
Check the lamb every 15 minutes and turn every hour. The butter should just cover the lamb; add more butter if necessary. Do not allow the butter to burn. If you need to sleep during this time, remove heat. After about six hours (you can remove the bone and) transfer the meat and the butter to a smaller saucepan which just fits and continue.
Serve (without the butter) with boiled potatoes and boiled vegetables or salad.
Note that ten hours cooking time is sufficient and that the lamb will shrink. Keep the leftover butter for other uses, such as frying. This is an adaptation of a Greek recipe.