1.Combine lamb, ginger, garlic, chilli, yoghurt, coriander, spices and salt in a medium bowl. Cover; refrigerate overnight.
2.Heat half the ghee in a large, heavy-based saucepan over medium heat; fry almonds and sultanas until browned lightly. Remove from pan with a slotted spoon.
3.Heat remaining ghee in same pan over medium heat; cook onion, covered, 5 minutes or until soft. Remove lid; cook another 5 minutes or until onion is browned lightly. Remove half the onion from pan.
4.Add lamb mixture to pan; cook, stirring, until lamb is browned lightly. Add the water; bring to the boil. Reduce heat; simmer, covered, over low heat, stirring occasionally, 1 hour. Remove lid; simmer, uncovered, a further 30 minutes or until lamb is tender. Season to taste.
5.Meanwhile, cook rice in a saucepan of boiling, salted water 5 minutes or until half-cooked; drain.
6.Combine saffron and milk in a small bowl; stand 15 minutes.
7.Preheat oven to 180ºC/ 350ºF.
8.Spread half the lamb mixture in an oiled 3.5-litre (14-cup) ovenproof dish; top with half the rice, then remaining lamb and rice. Drizzle saffron milk mixture over rice; cover tightly with oiled foil and lid. Bake 40 minutes or until rice is tender.
9.Serve biryani topped with reheated reserved onion, almond mixture and extra coriander.