FOR THE LAMB:
- 2kg leg of lamb
- 8 cloves garlic, peeled and cut into slivers
4 sprigs rosemary, leaves only
- 3 tablespoons extra-virgin olive oil
- 85g membrillo, extra, to taste
100ml dry white wine
- 50ml dry sherry
- 300ml lamb or chicken stock
FOR THE POTATO GRATIN
- 500g potatoes
- 500g celeriac
- 425ml double cream
- 140ml sour cream
- 85ml whole milk
2 cloves garlic, very finely sliced
- 2 sprigs thyme, leaves only
- 100g peeled, cooked chestnuts, vacuum-packed or in a jar 10g butter, for greasing
- Make deep incisions all over the lamb. Stuff a sliver of garlic into every incision followed by a few leaves of rosemary. Rub olive oil all over the joint and into the incisions. Put into a roasting tin, cover loosely with cling film and put in the fridge for a few hours to marinate.
- Bring the lamb to room temperature. Heat the oven to 200°C/fan oven 180°C/mark 6. Spread about half the membrillo on the underside of the joint and season with salt and freshly ground black pepper. Set into a roasting tin then spread with the rest of the membrillo, pushing down into some of the incisions. Season. Roast for 30 minutes.
- Meanwhile, make the gratin. Peel the potatoes and celeriac and slice very, very finely - a mandolin does this best. In a large saucepan, mix together the creams and milk and bring to just under the boil. Add the sliced vegetables, garlic and thyme and cook gently for 5 minutes. Slice the chestnuts. Season the vegetables really well then put half into a buttered gratin dish, spreading them evenly. Spoon the chestnuts on top then spread the rest of the vegetables on top.
- Turn down the oven to 180°C/fan oven 160°C/mark 4 and roast the lamb for another hour (for pink lamb). After 45 minutes add the wine and sherry, pouring them round the joint.
- Meanwhile, 15 minutes after turning the oven down, put the gratin in. When you add the alcohol to the lamb, check to see whether the gratin needs to be covered loosely with foil to stop it becoming too dark.
- When the lamb is cooked, put it on to a warm platter, then cover with foil and insulate with some towels so that it can rest for 15 minutes while the gratin finishes cooking and you finish the sauce.
- Put the roasting tin over a medium heat and add the stock. Bring to the boil and boil until it tastes as you like it - it shouldn't be so reduced that it's too salty. It doesn't matter if it's quite thin - the flavour is the important thing. The juices will be quite sweet because of the membrillo, but if you can't detect it add a little more and allow it to melt. Strain the sauce through a sieve before serving with the lamb.
To drink: To match the sweet note of membrillo, a fuller, fruitier, spicier red than for plain roast lamb, for example Ribera del Duero, Margaret River Cabernet Sauvignon, Languedoc or southern Rhône: Domaine de L'Espigouette Plan de Dieu 2011, £11.99, Wine Rack. Wine details correct at original magazine publication date.
From the Gourmet supplement in the December 2014 issue of House & Garden. Recipe by Diana Henry; photograph by Emma Lee; food preparation and styling by Jack Sargeson; table styling by Alexander Breeze; wine recommendations by Joanna Simon.