Heat a large glug of oil in a deep, flameproof casserole over a medium heat. Add the onions and fry for 4-5 minutes until beginning to colour. Add the garlic and all the ground spices and fry for 2 minutes more, stirring with a wooden spoon.
Season the lamb, then add it to the pot and cook for 5 minutes, stirring regularly. Add the chopped tomatoes, prunes, stock and sugar and bring to a good simmer, then reduce the heat to low. Add 100ml water and simmer gently for 3 hours. Stir the tagine every so often so it doesn’t stick and burn on the bottom. If it reduces and thickens too quickly, add a splash more water to loosen it. You want a rich sauce that’s still fairly liquid.
For the last 30 minutes of the cooking time, stir in the chickpeas and lemon juice. Taste and season with salt and pepper. Serve scattered with parsley, coriander, pistachios and pomegranate seeds, with couscous or flatbreads (you could try one of these flatbread recipes) as an accompaniment.
