Marinate the mutton with whipped yogurt, ginger, garlic and 3 tbsp mustard oil.
Refrigerate for at least 2-3 hours. Even better if this can be done the night before.
Add the remaining ingredients, give it a hearty mix, rub the marinade well over the mutton pieces. Some 10 mins or so. This step is key, the patience is well worth it.
Add 1 tbsp mustard oil to the hnaari, brush the oil lightly on all sides. Heat the greased empty hnaari over a low flame so as to season it. Allow to cool to room temperature.
Add the marinated mutton along with the marinade to the hnaari.
Put the lid on, seal with the dough.
Cook over a low flame for some 2.5 odd hours. Every 30 mins or so, lift the hnaari carefully from the flame and give it a shake, this shall prevent the curry from sticking to the bottom of the pot.
Remove from flame, give it a standing time of 15-20 minutes.
Break the dough seal gently, serve hot with steamed rice.