1. Preheat the oven to 220°C/200C fan/gas 7.
2. Scatter the onion, celeriac & garlic onto a roasting pan & sit the lamb on top, drizzle with olive oil & season generously.
3. Roast for 30 minutes, then add the tomato paste, rosemary & stock, cover with a tight-fitting lid & place back in the oven set at 160°C/140C fan/gas 3 for 4 hours or until tender.
4. Remove the lid & continue to cook for another 30 minutes.
5. Once cooked carefully remove the lamb & the veg then pass the juices through a fine strainer into a clean saucepan & boil to a rich, unctuous gravy skimming the fat as it rises to the surface, at this point you can thicken the juices with a little cornflour mixed with cold water if desired then fold through the butter beans, lemon zest & juice & parsley.
6. Pour back over the lamb & vegetables & serve straight away.

Using two forks pull the meat away from the bone & serve with boiled potatoes & crusty bread.