Ingredients

• 100g/4oz butter
• 2 large onions, finely chopped
• 1 tbsp fresh thyme, chopped
• 3 bay leaves, crumbled
• 6 garlic cloves
• 2kg/4½lb floury potatoes, sliced and soaked in cold water
• 2kg/4½lb leg or shoulder of lamb
•   seasoning

Method

1. Preheat the oven to 230C/450F/Gas 8. Use 25g/1oz butter to grease a large earthenware gratin dish. Mix onions, thyme and bay leaves, three chopped garlic cloves and seasoning.
2. Cover the bottom of the dish with a layer of drained potatoes and sprinkle over some of the onion mixture. Continue making layers, finishing with a layer of potatoes, then cover with warm water. Cut 25g/1oz butter into cubes and dot over the potatoes; cook for 30 minutes.
3. Meanwhile, prepare the lamb. Smear the rest of the butter over the joint. Slice the remaining cloves of garlic and tuck them under the skin or in slits in the lamb's flesh. Reduce the oven to 200C/400F/Gas 6.
4. Place the joint on top of the potatoes and cook for 1½ hours, turning halfway through cooking, until most of the liquid has been absorbed into the potatoes and the meat is tender. If you like your meat well done, cook for slightly longer.
5. Transfer the joint to a warm serving dish and allow to rest for 15 minutes. Leave potatoes in the oven to crisp. Use the meat juices for gravy.

Notes