Prepare the Oil: Heat mustard oil in a heavy-bottomed pot until it reaches smoking point. Splash in the strained garlic water and immediately cover with a lid. This softens the oil and removes its bitterness.
Sauté Aromatics: Add bay leaves, black cardamom, and cloves. Add sliced onions and fry until they are light golden brown.
Brown the Meat: Add the mutton pieces. Sauté on medium-high heat until the meat changes color. Add ginger-garlic paste and roast (bhunai) for 5-7 minutes.
Add Yogurt Mix: Whisk the yogurt with red chili powder, coriander powder, and turmeric. Pour into the pot. Cook until the oil separates from the masala.
Slow Cook: Add 2 cups of water. Cover and cook on the lowest heat for 2-3 hours until the meat is 90% tender. (Alternatively, pressure cook for 4-5 whistles).
Thicken: Mix wheat flour with water to make a smooth, lump-free slurry. Stir it into the gravy along with the black pepper and kewra. Add your secret Nihari Masala now. Let it simmer for another 20 minutes on low heat.
Final Tempering (Rogan): In a separate pan, heat desi ghee. Add the coarse leftover spices and Kashmiri chili powder. Strain this red oil (Rogan) directly over the Nihari.
Rest and Serve: Let the Nihari rest for 10 minutes for the flavors to settle. Garnish with ginger and green chilies.