Slow Roasted Rosemary Lamb with Boulangère Potatoes

1. One hour before you want to cook it, take the lamb out of the fridge to allow it to come up to room temperature. Preheat the oven to 140°C/Fan 120°C/Gas 1. Fill and boil the kettle.

2. Thinly slice the potatoes into rounds – roughly 2mm thick. Trim, peel and finely slice the onions. Finely chop the leaves from half of the rosemary sprigs. Add the potatoes, onion and the chopped rosemary to a large mixing bowl. Peel the garlic cloves and finely slice them. Add half of the sliced garlic to the potatoes. Stir well to mix. Arrange the veg in a large roasting tin.

3. Place the lamb, skin side up, on a board. Use a small, sharp knife to pierce the lamb all over. Stuff a slice of the remaining garlic and rosemary leaves into each hole. Drizzle over 1 tbsp olive oil. Season with a pinch of salt and pepper.

4. Add the vegetable stock powder to a heatproof jug. Pour over 400ml hot water. Stir well to mix. Pour the hot stock over the potatoes. Dice the butter into small cubes and dot over the potatoes.

5. Place the lamb on top of the potatoes. Cover the roasting tin with foil. Place the tin in the oven and roast for 4 hrs, basting the lamb regularly with the stock from the dish till the lamb is tender.

6. When the lamb has roasted for 4 hrs and is tender, increase the oven to 200°C/Fan 180°C/Gas 6. Remove the foil and roast for a 30 mins till the lamb is golden brown and the potatoes are cooked through.

7. Remove the tin from the oven, cover with foil and leave the lamb to rest for 20-30 mins before serving with the redcurrant jelly.