Keep an old pan on heat for preheating (to keep the biryani pot on it for dum cooking).
Take a large non stick pan and add the mutton gravy as first layer (preserve some gravy if you find it in excess). Now spread half of the cooked rice evenly and loosely over the gravy without pressing it.
Sprinkle the coloured milk (2 to 3 tsp), fried onion, garam masala powder, shahi jeera and chopped herbs.
Spread rest of the rice and repeat the step 4.
Finally, pour melted ghee or butter and make big deep dents into the rice so that the steam can come to the surface. Cover the pot with an aluminium foil and place the lid in a way that no steam escapes. Place the biryani pot on the preheated hot pan and cook on low flame for about 15 minutes.
When you see that the foil is up with lot of steam, switch off the flame and keep the biryani covered for another 10 minutes.
After 10 minutes open the lid and serve the biryani hot with Raita