Heat ghee in a large heavy kadhai or wok over high heat. Add minced onions and fry till translucent. Add ginger paste and garlic and fry till brown. Stir well to ensure that the masala does not burn.
Add green cardamoms, black cardamom, black peppercorns, cloves, and garam masala, and give it a good stir. The kadhai should be smoking hot.
Quickly slide in minced mutton, stir, and add mutton pieces. Stir to mix evenly with the onion masala. Sprinkle in turmeric, red chilli powder and salt. Cook till mince and mutton have darkened in color, about 20 minutes.
Transfer the mixture to a pressure cooker and place on high heat. Add chopped tomatoes, continuing to stir well for 2-3 minutes. Add water to cover, bring to boil, then seal it with the pressure cooker lid. After whistle, turn down the heat and cook for about 15 minutes. Remove from heat and let it cool till the pressure has subsided before opening the cooker.
If the consistency of the curry is too thin, return uncovered pressure cooker to stove and cook for another 5-10 minutes. The curry should have a consistency of medium thick gravy. Check seasoning and add salt if needed.
Allow the korma to rest for a few minutes before serving.
Garnish with ginger juliennes and serve with naan or lacchha parathas.