Method

1. Rinse and trim the lamb and place in a large baking dish.

2. Preheat oven to 220c.

3. Cut the lemons and squeeze the juice all over the lamb, rubbing the skins over the meat.

4. Season with salt, pepper and herbs and dot with butter.

5. Bake for about 30 minutes, turning once or twice, until browned all over.

6. Add 300ml water to the baking tray and cover tightly with foil.

7. Reduce the oven temperature to 180c and cook for a further hour.

8. Cut the potatoes into chunks and scatter around the lamb in the baking tray, shaking to coat them with juices. Recover the tray and cook for a further hour.

9. Remove the foil and cook uncovered for another 30 minutes to crisp the potatoes.