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    Lamb on a Rack with Two-potato Gratin and Garlic and Onion Sauce

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    Lamb on a Rack with Two-potato Gratin and Garlic and Onion Sauce

    Placing the lamb on a rack allows the meat to roast rather than stew in the moisture released by the cooking process, and the potatoes benefit from the flavours of the tasty meat juices, too.

    • Preparation time: 40-45 minutes, plus at least 30 minutes marinating time
    • Cooking time: About 1½ hours for pink (medium) meat, plus 15 minutes resting time (see 'Cook's Tips')
    • Total time: 2 hours 10 minutes to 2 hours 15 minutes, plus marinating and resting time 60 minutes 60 minutes 15 minutes

    Serves: 6


    • 1 large whole bulb garlic
    • Grated zest and juice of 1 organic lemon
    • 4 tbsp olive oil
    • 1 pack fresh rosemary
    • 1.6-1.8kg Waitrose Farmhouse Dorset Breed Whole Leg of Lamb
    • 2 red onions, finely chopped
    • 400ml whole milk
    • 1 lamb stock cube
    • 3-4 large potatoes, about 600g, such as King Edward, peeled and sliced
    • 2-3 large sweet potatoes, about 400g, peeled and sliced
    • 1 large shallot, finely chopped
    • 150ml dry white wine
    • 2 tbsp single cream (optional)
    • Sea salt
    • Freshly ground black pepper


    1. To blanch the garlic, separate the cloves without peeling them. Reserve 2 cloves and place the rest in a small saucepan of boiling water for 5 minutes. Drain, cool, then slip off the skins. Set aside.
    2. To make the marinade, take 1 of the 2 uncooked garlic cloves and crush in a bowl. Mix with the lemon juice and 2 tablespoons of the oil. Reserve a few sprigs of rosemary for the garnish, then snip half the remaining rosemary into the marinade and season with pepper. Place the lamb on a plate, rub the marinade into the meat, then cover with clingfilm and leave to marinate for at least 30 minutes. If marinating for longer, place in the fridge, allowing 30 minutes-1 hour for the lamb to come back up to room temperature before placing in the oven.
    3. For the sauce, place the red onion, blanched garlic and milk in a small pan and bring to a simmer. Crumble in the lamb stock cube, add the lemon zest and cook over a very low heat for 10 minutes until the onion is soft, stirring frequently and making sure the milk doesn't boil over. Set aside until cool enough to pour into a liquidiser, then blend until smooth. Adjust the seasoning, return to the pan and set aside.
    4. Preheat the oven to 200°C, gas mark 6. Cut the remaining uncooked garlic clove in half and use it to rub the base and sides of a large roasting tin. Arrange all the potatoes in the tin with the shallot. Snip the remaining rosemary over, pour in the wine and drizzle with the remaining oil. Season. Place the lamb on a large cooling or oven rack. Season with salt. Place the rack with the lamb over the tin.
    5. Cook for 1½ hours for pink meat, turning twice during cooking. Skim off any excess fat from the potatoes.
    6. Remove the lamb and potatoes from the oven, place the lamb on a carving board and discard the rack. Cover the meat loosely with foil and rest for 15 minutes in a warm place before carving. Add a few tablespoons of the potato gratin juices to the garlic and onion sauce, then reheat gently until piping hot. Stir in the cream, if using, and season. Gently stir the potatoes and return to the switched-off oven to keep warm.
    7. Carve the lamb into thin slices and arrange on a large serving dish, with a little of the sauce poured over. Garnish with the reserved rosemary. Pour the remaining sauce into a warmed jug and serve the potatoes in their roasting tin.

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    Cook's tips

    For pink meat, cook the lamb for 20 minutes per 500g plus 25 minutes; if you prefer it well done, cook for 25 minutes per 500g plus 25 minutes.

    The two-potato gratin can be prepared up to 3 hours ahead - keep it covered with clingfilm and chilled in the fridge


    Average user rating

    4 stars