Heat the ghee in a large saucepan over medium heat. Place the lamb in the pan and cook until evenly brown. Season with allspice, cinnamon, cloves, nutmeg and cardamom.
Place a layer of onion on top of the lamb in the pan, followed by layers of potato, aubergine, courgette and tomatoes. Do not stir. Place the chilli in the centre of the vegetables. Season with salt. Mix the tomato puree and water and pour over the vegetables. Bring to the boil, reduce heat to low and simmer 1 hour, until vegetables are tender.
With a mortar and pestle, crush together the garlic, salt and mint. Mix with 2 tablespoons of liquid from the pan and pour over ingredients in pan. When removing the mixture to the serving dish - a fairly open or wide bowl - tip the pan and let it slide out the side so that it stays in the layers.