Persian lamb tagine

Name: Persian lamb tagine
Ingredients: 2kg lamb neck fillets; 5 tbsp mild olive oil or sunflower oil; 3 medium onions cut into thin wedges; 4 garlic cloves finely chopped; 4 tsp ground cumin; 4 tsp ground coriander; 1 tsp hot chilli powder; 1 tsp ground turmeric; large pinch of saffron; 2 cinnamon sticks; 2 preserved lemons (from a jar), drained and cut into thin wedges; 300g ready-to-eat dried apricot; 250g ready-to-eat dried pitted dates; 100g shelled pistachios; 2 tsp rosewater; 25g cornflour; small bunch coriander leaves roughly chopped; cooked couscous or basmati rice, to serve