Beer-roast lamb with a parsnip gratin
For the lamb
*2.5kg (large) leg of lamb, part-boned and tied with string *500ml pale or golden ale
*300ml chicken or lamb stock
*8 cloves garlic, skin on, bruised
*2 tbsp chopped rosemary
*2 tbsp olive oil
*1 bunch baby or young carrots, scrubbed with any tops trimmed *2 red onions, thickly sliced
*3 rosemary sprigs
For the gratin
*400g crème fraîche
*200ml milk
*butter for greasing *1kg parsnips, trimmed, peeled and finely sliced into rounds
(preferably with a mandolin) *100g gruyère cheese, grated *1 tbsp chopped rosemary *a good grating of nutmeg
Put the lamb in a large, sturdy food bag or non-metallic dish and cover with the ale and stock. Add the garlic and rosemary and leave to marinate for 8-48 hours. Once ready to cook the lamb, preheat the oven to 180°C/gas mark 4.
To make the gratin, combine the crème fraîche and milk in a bowl and season lightly with salt and pepper. Butter a medium baking dish and cover the base with one third of the sliced parsnips and one third of the cheese. Season with salt, pepper, a little rosemary and a little nutmeg. Spoon one third of the crème fraîche mixture over and cover with another layer of parsnips and cheese. Repeat the layering, reserving the last third of cheese to scatter over the top of the gratin. Cover tightly with foil and slide into the oven for 40 minutes.
Lift the lamb leg from the marinade and pat dry. Rub the olive oil over the leg, season generously with salt and pepper and lay it in a large baking dish or sturdy roasting tin large enough to contain the beer and stock. Roast (without the marinade), for 30 minutes, until beginning to brown. Spoon any excess fat from the lamb dish and discard, then add the marinade, carrots, onions and rosemary sprigs to the dish, along with 150ml water. Cover tightly with two layers of foil and turn the heat down to 120°C/gas mark 1.
At this point, remove the gratin and set aside. Cook the lamb for 6-6½ hours, until the meat is incredibly tender. Check after 4 hours and add a little more water if the liquid has reduced to almost nothing. Remove the lamb from the oven and cloak with a couple of tea towels. Rest for 40 minutes.
Turn the oven up to 190°C/gas mark 5 and slide the parsnip gratin back in. Bake, covered, for 30 minutes, then uncover and cook for a final 5-10 minutes, until golden on top and bubbling. Serve with the lamb and plenty of steamed, buttered greens.