Add meat in a large pot of salted water (I add 1 tablespoon of salt at this stage) with black cardamom, cloves, cinnamon stick, cumin seeds, 2 sliced onions, and 1 tablespoon of crushed garlic. Bring to boil, cover pot and simmer on low heat until mutton is tender, about 1 ½ to 2 hours.
Once the meat is tenderized, remove the meat with a slotted spoon, and set aside.
Strain the bone broth, and set aside.
In a large pot, heat oil. Once the oil begins to shimmer, add the remaining sliced onion, and fry for about 15 minutes on medium-low heat or until a deep golden brown.
Add crushed garlic, and fry for roughly 30 seconds or until fragrant.
Add the mutton, salt, and fry for 8-10 minutes on medium-high heat.
Add 6 cups of the strained mutton broth to the pot. Check for salt, and bring to a boil. You can put the leftover of the broth in airtight containers, and freeze for later use.
Add rice, and let the water boil out, about 10 minutes.
Once the water boils out, wrap lid with a clean kitchen towel and place it securely on the pot. Let rice steam on very low heat for 10 minutes.
Place pulao on serving platter and fluff with a fork.