There are variants of this published elsewhere, but with timings, temperatures and instructions that simply don’t work for me. I blame publishers’ timetables and the lack of decent testing and copy editing, rather than the authors.
Anyway, this is a handy dish as you get the meat and spuds out of the way up front, giving you a chance to get on with everything else. The layer of skin, fat and connective tissue on top, combined with the steam from the stock below, will keep the meat moist for the long cooking period.
To feed six you will need:
- a whole shoulder of lamb, bone in: this will be around two kilos
- a kilo of potatoes: the floury sort, e.g. King Edward, work the best
- one large or two medium brown onions
- a whole head of garlic (or more if you want)
- a fistful of herbs (fresh thyme is best, however, if you use rosemary, then just half a dozen stalks, as it’s a bit of a bully)
- around 800mL stock (chicken or vegetable)
- salt, pepper, bay leaves
Start with the spuds. You’ll need to peel them and slice them to around an eighth of an inch in thickness. I use a mandoline for this. Ditto the onion. Put a layer of potatoes at the bottom of a large roasting tin, then the onion in a single layer, a couple of bay leaves, and a grind of pepper, and just a touch of salt. Continue to layer the potatoes on top: it needs to be even but not pretty. The combined potato and onion layer should be around an inch deep in total. Pour over the stock, it should almost, but not quite, cover the potato. (Just top up with water if you don’t have enough stock.) Spread the herbs in a layer on top of the potato.
Pre heat the oven as high as it will go.
Use a sharp knife to score the very outside of the joint in five or six long cuts, about two inches apart. (That’s the convex side, with membrane or possibly skin depending on how real your butcher keeps it.) Rub some salt into the cuts. Dismember and peel the garlic, and using a sharp knife, make holes in the underside (that’s the concave side) of the joint, and insert the garlic cloves. Or, if you’re feeling lazy, just spread the cloves on top of the herbs.
Put the whole lot in the oven, leaving it at maximum for five minutes before reducing to gas mark 2, which is around 150°C in my oven. Fan ovens probably need to be around 135°C.
It will need five hours. Check every hour or so, and don’t be afraid to top up the liquid if it seems to be drying out. It is almost impossible to overcook this, the risk is undercooking. After about two hours the stock should be glooping gently, and the joint softly hissing at the fat runs out from under the skin and gently bastes the meat. At the end of the fourth hour, slide a skewer into the thickest part of the joint. If you’re met with a lot of resistance, you may need to turn the oven up a notch.
(If you just happen to have about a kilo of parboiled carrots and parsnips tossed in a couple of tablespoons of duck fat or butter, and lightly seasoned, slide them into the oven on the shelf beneath the meat at this point.)
By the end of hour five, a skewer inserted into the thickest part of the joint should meet with no resistance at all, and the job is done. Remove the tray from the oven, cover with foil, and leave to rest for twenty minutes.
(The theoretical carrots and parsnips should be removed, doused with two tablespoons of honey, tossed, and returned to the oven, set again to maximum, whilst the meat rests. Sprouts with pancetta and chestnuts would complete the picture.)
Dish up. You should be able to carve the lamb with a spoon. Try not to fight over the potatoes.