In a bowl, infuse the saffron in 2 tablespoons of hot water. Leave aside
In a mortar, grind the cardamom seeds and mace into a powder with the pestle then set aside.
Cut 2 of the onions into slices. Season with salt and leave aside for 20 minutes. Remove any excess water from the onions then dry with kitchen paper. Heat the oil over high heat and deep-fry the onions until they become golden. Transfer from the pan onto kitchen paper to drain any excess oil. Leave half of the onions aside.
Process the other half with 3 tablespoons of hot water until it forms a paste.
Shred half of the ginger, thinly. In a large bowl, mix with the garlic, chilli powder and lime juice. Add the onion paste and the lamb. Stir well then marinate for about 1 hour.
Cut the other 2 onions into dice. Pour the vegetable oil into a large casserole then heat over medium heat. Fry the onions until tender for about 5 minutes. The onions should not brown.
Cut the rest of the ginger into thin strips. Leave aside. Add the green and black cardamom, cinnamon, cloves and bay leaves to the onions and cook for about 30 seconds.
Stir in the meat, marinade, garam masala, green chillies and ginger strips then bring to an almost boil. Pour in the yogurt, tablespoon by tablespoon. Place a lid over the pan and stew for about 45 minutes, until the lamb is soft and the sauce has reduced.
Soak the rice in cold water for about 20 minutes. Ten minutes before the meat is cooked, pour enough water in a large pan, add some salt and bring to the boil. Strain the rice then put into the boiling water and cook for about 5 minutes, until half-cooked. Strain again.
Heat the oven to 160°C. Place half of the lamb into another casserole and layer with half of the rice. Top with half of the ground mace and cinnamon and half of the mint.
Cover with the rest of the meat and rice. Sprinkle with the remaining spices, the mint and the browned onions from the beginning of the recipe. Add a few butter pieces on top and sprinkle with the saffron and saffron-infused water. Cover with wax paper and a lid.
Put in the oven for about 40 minutes, until the rice is well cooked. Lightly mix up the rice using a fork and serve while hot.