Heat your oven to 140°C/Fan 120°C/Gas 1. Peel and crush or grate the garlic. Finely chop the rosemary leaves. Combine them in a bowl with 1 tbsp olive oil and a good pinch of salt and pepper. Set aside.

Peel and finely slice the onion. Scrub and trim the carrot, then slice it on the diagonal into 1cm-thick rounds. Trim the dry ends off the celery and slice it to match the carrots and onions. Scoop all the veg into a small casserole dish or a roasting tin.

Unwrap the lamb (keeping the string on to hold it together) and pat dry with kitchen paper. Slash the flesh and fat all over with a small, sharp knife. Rub in the garlic and rosemary paste. Pop the lamb on top of the veg.

Crumble half the stock cube into a heatproof jug. Stir in 300ml boiling water to dissolve the stock. Pour the stock around the lamb but not over it. Pop on the lid or use foil to cover the roasting tin, scrunching it to the sides to seal it well. Slide the lamb into the oven and slow roast for 3 hrs.

After 3 hrs, take the lamb out of the oven and turn the temperature up to 180°C/Fan 160°C/Gas 4. Take the lid or foil off the dish and return to the lamb to the oven to cook, uncovered, for 30 mins.

Lift the lamb out of the dish and let it rest on a board, loosely covered with foil, for 20-30 mins. While the lamb rests, skim as much fat as you can off the top of the casserole juices. Use a masher or fork to crush the veg in the stock to make a thick sauce. Taste and adjust the seasoning if you think it needs it.

Snip off the string. The lamb should be tender enough to fall apart, so shred it with 2 forks, then scoop the lamb back into the dish and stir to mix with the vegetable sauce. Warm gently over a low heat for a few mins, then serve.