Heat the fireplace or chulha or gas oven, heat a brass kadai or any wok you like to use for the cooking.
Add the mustard oil and heat it.
Now, add all the whole spices like Cinnamon Stick, cardamom, Cumin, Bay Leaf, Cloves, Black Pepper.
(Pro Tip: Let the whole spices sizzle briefly in mustard oil to release their aroma without burning.)
Add the chopped onions, fry it lightly and add the mutton pieces.
Stir the 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 salt.
Sauté it for 10 mins. Cover it with a lid so that the water comes out from the mutton.
Add the Nutmeg, javitri, roasted masala powder and the beaten yogurt, and mix it nicely so that the yogurt does not have any bubbles in it.
(Pro Tip: Add beaten yoghurt gradually and stir continuously to prevent curdling in the hot masala.)
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.
(Pro Tip: Keep the mutton at a gentle simmer).
After 25 mins add the garam masala and stir it well. By this time, the mutton will get well cooked, and your Mutton Kosha will be ready.