In a small bowl, combine cinnamon, cardamom and cumin. Stir well and set aside.
Rinse the rice vigorously in five changes of water (or under running water until it runs clear). Combine rice with 8 cups water and 2 tbsp salt. Let soak at room temperature for at least 2 hours.
In a large, heavy pot, heat 2 tbsp oil over medium-high heat. When it shimmers, add the minced onions and saute until limp and golden, about 8-10 minutes. Add the lamb, 3/4 tsp salt, a large pinch of black pepper, turmeric, cinnamon and 1/2 tsp of the spice mixture from step 1. Saute 5 minutes. Add 2 cups water, bring to a boil, reduce to a simmer, cover, and cook until meat is tender, 2 1/2-3 hours.
About 30 minutes before the meat is ready, prepare the lentils and rice. Combine lentils with 3 cups water and 1/2 tsp salt, bring to a boil, and simmer 10 minutes, then drain.
In a frying pan, heat remaining 2 tbsp oil over medium heat until shimmering. Add sliced onion and saute until soft and golden, about 8 minutes. Add raisins and dates, saute another 2 minutes, then take off heat and set aside.
Bring 2 qt water and 2 tbsp salt to a boil in a large (4-pt) nonstick pot. Add drained soaked rice and parboil 3-5 minutes, until grains are firm but no longer brittle. Drain rice and rinse under hot water.
In the same pot, melt butter. Transfer half of it to a small bowl and set aside. Mix half the rice with the yogurt and spread it in the bottom of the pot (on top of the butter). Sprinkle rice with a layer of lentils, then a layer of onion-and-fruit mixture, also sprinkling remaining spice mixture between layers. Fluff remaining rice and repeat layering until all ingredients are used up; reduce the diameter of each layer so it forms a rough cone/pyramid.
Cover and cook over medium heat 10 minutes to form a nice crust on the bottom. Remove the cover, drizzle reserved melted butter over the contents, lay a dish towel over the top of the pot, re-cover and cook over low heat 50 minutes. Without moving the lid, set the pot on a cold, wet dishtowel on the counter for 5 minutes (to loosen the crust).
Transfer rice-and-lentil mixture to a serving platter, again forming a cone or pyramid shape. When only the crust remains in the pot, dislodge it with a knife or spatula and serve separately; it is considered a sign of good luck to get it out in one piece. Spoon the lamb stew around the pile of rice and serve.