Ingredients

Step by step

1. Preheat the oven to 190°C, fan 170°C, gas 5. Put the lamb into a large roasting tin and season the meat.
2. Halve the heads of garlic through the middle and add to the tin. Juice 3 of the oranges and add that too. Cover the tin with foil and transfer to the oven for 2 hours.
3. Drain the tomatoes (save the oil to use in salad dressings). Slice the chorizo thickly and slice the remaining orange into wedges. Tip the potatoes onto a large baking tray, add the bay leaves, if using, and drizzle with the oil; season and toss.
4. After the 2 hours, remove the foil from the tin, baste the lamb with the tin juices and scatter the tomatoes, chorizo and orange wedges around the lamb. Return to the oven, uncovered, for a further hour. Put the potatoes in the oven at the same time on another shelf for 1¼-1½ hours, giving them a shake from time to time, until golden and tender.
5. Lift the lamb out of the tin and onto a board, cover it with foil, ready for carving – it will be fine to leave for 30 minutes or so to rest.
6. Then, using a slotted spoon, transfer the other ingredients from the tin, including the orange wedges, to a dish or large platter and keep warm. Using a large spoon, skim the fat from the juices, there will be a lot but it is easy to see as it will have separated and sit on the top of the juices (or tip them into a jug, drain off the fat and then reheat).
7. Put the tin over direct heat and bubble the juices for a few minutes, tasting them and adjusting the seasoning as necessary. Chop the parsley and stir it in.
8. Tip the potatoes into a serving dish. Now, either return the lamb and other ingredients to the tin to carve at the table, or carve the lamb and arrange the slices on a platter with the other ingredients; serve drizzled with some of the cooking juices and pour the rest into a jug for everyone to help themselves. Serve with the roasties.