Grind half of the onions, half of ginger and 4 garlic cloves in a mixer or spice grinder along with 1 tbsp mustard oil into a smooth paste.
Dry roast coriander seeds and cumin seeds and grind them coarsely.
Marinade the mutton pieces with the onion-ginger-garlic paste,2 heaped tablespoon yogurt, 1 tsp of kashmiri mirch powder, 1 tsp cayenne, turmeric powder, coriander powder, cumin powder and pinch of salt.Add chopped tomatoes. Mix well. Refrigerate the marinade for atleast 2 hours or leave it overnight.
Wash, clean and peel the potatoes and chop it into cubes. Add it to chicken marinade 20 minutes before cooking.
Finely chop the remaining onions, ginger and garlic. Heat a pressure cooker. Add 1.5 tbsp oil into it and when the oil is hot, add bayleaf, cardamon pods, cloves, black peppercorns and cinnamon stick. Saute it for 5 minutes on low heat till the spices release their aroma.
Add the remaining chopped onions-ginger-garlic, green chillies and saute till the onions become soft, brown and translucent.
Now add the marinaded mutton along with potaties and saute at medium heat for 20-25 minutes .
Add 1 1/3 cup warm water, remaining kashmiri mirch and salt as per taste. Cover the lid of the pressure cooker with whistle on. Cook on medium high heat till the pressure cooker gives two whistles. Lower the heat and cook for another 35-40 minutes. Turn off the heat and allow the steam to cool.
Remove the lid of the cooker. Add garam masala and a teaspoon of ghee. Stir and mix. Close the lid of the cooker until ready to serve.
Transfer the pathar mangsho curry into a serving bowl. Serve it hot with ruti or chappati or as a side dish along with rice.