Heat the fireplace or chulha or gas oven, heat a brass kadai or any wok you like to use for the cooking.
Add oil and heat the wok.
When the oil is hot, add all the whole spices like Cinnamon Stick, Cardamon, Cumin, Bay Leaf, Cloves, Black Pepper.
Add the chopped onions, fry it lightly and add the mutton pieces.
Stirring mutton nicely.
Add ginger garlic paste and stir fry it. When the raw aroma of the ginger & garlic paste goes out then add all the powder masalas like Turmeric, Kashmiri Red Chili Powder, Red Chili Powder, Sugar, Coriander, Dry Chili, Cumin, Coriander, Cumin and half spoon salt.
Sauté it for 10 mins. Cover it with a lid so that the water comes out from the mutton.
Add Nutmeg as required and the beaten yogurt, and mix it quickly so that the yogurt does not get bubbles in it.
Keep it for 5 mins and add lukewarm water (if you give normal water then it will slow the boiling process) as required to cook the mutton.
Cook it on low heat. After 25 mins add the garam masala and stir it well. By this time the mutton will get well cooked and your Mutton Kosha is ready. Serve it steamed rice, pulao, roti, naan, or paratha.