Marinate the mutton pieces with raw papaya paste, curd, salt, chilli powder and biryani masala for 4 hours in the refrigerator. Also soak the basmati rice in water for half an hour.
Wash the rice and boil it in water with whole garam masala and a few drops of oil. The rice should be cooked 75%. Strain the rice and let it cool down in a plate. (The rice should be fluffy and shouldn't stick to one another.)
Now take oil in a pressure cooker. Saute the onion, ginger and garlic. Then add the marinated mutton and cook on slow flame for almost half an hour. Pour little water and pressure cook the mutton for 4 to 5 whistles, till the meat is tender.
To prepare the dum biryani, take a large aluminium foil tray. Grease it with ghee. Pour half of the mutton in and add a layer of rice on top. Add a few drops of saffron soaked milk, rose water, biryani essence, fried onions and mint leaves.
Repeat the above process. Cover tray with an aluminium foil. You may bake it in the oven at 350 degree for half an hour.
If you are cooking on gas, you may use a heavy bottom wide container. Follow the same procedure and cover tightly by sealing all the edges. Cook on high flame for 5 minutes and then on low flame for another 20 minutes.
Do not put the container directly on gas. Place another heavy bottom flat tawa underneath your biryani container.
Serve hot biryani with curd/ raita or any other side dish.