1 Preheat the oven to 200°C (400°F) Gas Mark 6. Butter a roasting tin or baking dish large enough for the lamb to sit happily on top of the potatoes, which should come up to about 2.5 cm (1 in) below the rim. Trim the lamb of any excess fat and with a small knife, stab it on both sides at random intervals and stuff with bits of garlic and roughly torn anchovy.
2 Cut the potatoes into thin discs. (The easiest way of doing this is by using the slicing disc of a food processor if you have one, which only takes minutes, or a mandolin.) Cut the onions in half and slice them thinly in the same way. In a large bowl mix the potatoes and onions together well with the rosemary or thyme and season with ½ a teaspoon of salt and some black pepper.
3 Tip the potato mixture into the buttered dish or roasting tin, level it out evenly and place the lamb on top, pushing down a little to nestle it into the potatoes. Smear the lamb with the softened butter and season with salt and freshly ground black pepper.
4 Pour the hot stock or water into the dish and cook for 3 hours. If after the first two hours or so the lamb and top layer of potatoes are deep golden brown and crispy, turn the oven down to 190°C (375°F) Gas Mark 5 and loosely lie a sheet of tin foil over the top for the rest of the cooking time. Serve with redcurrant jelly and mint sauce.
Prepare the lamb to the end of Step 1 up to a day ahead. Cover and keep in the fridge. Bring back to room temperature at least an hour before cooking.
• The cooked lamb will happily keep for up to an hour somewhere warm.
• Delicious with Creamed Spinach, a plain green vegetable or a large bowl of salad.
• Mint Sauce: You can’t beat freshly made mint sauce with lamb. The vinegar cuts through the fattiness of the meat and the mint lifts it and adds brightness and zing. Chop a bunch of mint and mix in a small bowl with a tablespoon of granulated sugar and a pinch of salt. Pour over boiling water to barely cover and stir until the sugar has dissolved. Add white wine vinegar to taste, around 3 – 4 tablespoons.