For a more intense flavour, marinate the lamb overnight before slow-roasting. Begin this recipe a day ahead to drain the yoghurt.
150 gmGreek yoghurt1 cup(loosely packed) coarsely chopped coriander2 tbsp eachcoriander and cumin seeds, and sumac, plus extra sumac to serve6garlic cloves2lemons, rind finely grated, lemons thinly sliced2 tbspolive oil1lamb shoulder (about 1.8kg)Israeli couscous2 tbspolive oil2onions, thinly sliced3garlic cloves, thinly sliced½ tbspcumin seeds, coarsely crushed300 gmIsraeli couscous550 mlchicken stock80 gmbarberries or currants1 cup each(loosely packed) coarsely torn mint and parsley
For labne, place yoghurt in a fine sieve lined with muslin and placed over a bowl. Cover and refrigerate overnight until thick (discard liquid).
Preheat oven to 220C. Pound coriander, spices, garlic, rind and 2 tsp fine sea salt with a mortar and pestle to a coarse paste, then mix in oil. Make incisions in lamb at regular intervals with
a small sharp knife and rub paste all over lamb. Layer lemon slices over the base of a deep oven dish, place lamb on top, pour 250ml water into the pan and roast for 30 minutes. Reduce heat to 120C, cover pan with foil and cook, basting occasionally, until very tender (7 hours). Remove foil for last hour of cooking to crisp the skin.
For Israeli couscous, heat oil in a large saucepan or casserole over medium-high heat, add onion and sauté until golden and tender (8-10 minutes). Add garlic and stir until starting to colour (1 minute), then reduce heat to medium, add cumin and couscous, and stir until couscous is lightly toasted (3-4 minutes). Add stock, reduce heat to low, cover and cook until stock has been absorbed (20-22 minutes). Set aside covered to steam for 15 minutes. Season to taste, add remaining ingredients, reserving some herbs, then serve with hot lamb scattered with remaining herbs and labne sprinkled with sumac to the side.