In a blender combine cashews, red chili peppers, gingerroot, and cold water; mix at high speed for 1 minute.
Add cinnamon, cardamom, cloves, garlic cloves, poppy seed, 1 tbsp coriander, and cumin.
Blend again until smooth; set aside.
Place saffron in a small bowl, pour in boiling water, and soak for 10 minutes.
In a heavy skillet, heat butter over moderate heat.
Add chopped onion and cook for 7 to 8 minutes, until soft and golden brown.
Stir in salt, the cashew mixture, and yogurt.
Stirring occasionally, cook over moderate heat for 2 minutes.
Add cubed lamb, tossing to coat evenly.
Stir in the saffron mixture, reduce the heat to "low", cover tightly, and cook for 20 minutes, stirring often.
Sprinkle 1 tbsp coriander on top, cover, and cook for 10 minutes, or until the lamb is tender.
Ready in 1 hour.