Tie up the black cardamom, cinnamon, green cardamom and cloves in the Muslin cloth to make the spice bag and keep aside.
Heat 2- 3 cups water in a pressure cooker and add the spice bag and mutton pieces. Let cook for 2-3 whistles only or till mutton is almost tender. Be careful , do not overcook as we will be frying the mutton pieces later.
Drain out the mutton. Reserve the liquid and fish out the spice bag.
Take a portion of the beaten curd and add besan to it(this ensures that curd does not curdle). Add in the remaining curd and blend well in a blender.
In another pan add the remaining oil and flash fry the mutton pieces gently. Keep aside.
Take a heavy pan next and add in half of the oil. Add the onions and garlic and saute till pink but NOT browned, as the yakhni is essentially white in colour.Make a fine paste out of these, so that they are no where visible in the yakhni.
Add the onions back in the pan along with the curd. At this stage you have to stir the yakhni continously so as to avoid lumps. Once slightly thick add in the mutton pieces as well as the reserved liquor in which the mutton was boiled.
Add fennel seed powder, bay leaves, ginger powder, salt, black pepper, mint and kasuri methi. Cover and cook for 10-15 minutes and serve hot.