Take a large thick bottom vessel for dum cooking. And pour the gravy as the first layer.
Keep the fried fish over it as the second layer.
Spread half of the cooked rice over the meat and drizzle half of the milk, half of the fried onion (a handful), half of the chopped coriander, half of shahi jeera.
Repeat the step 12 with remaining cooked rice and dum ingredients.
Make a deep 2 or 3 dents in the rice so that the steam can circulate easily within the vessel.
Pour some ghee or butter over the rice and seal the vessel with a foil and a tight lid. (to avoid the steam from escaping)
Cook on medium-low heat for 15 minutes. You will see the foil has puffed up due to the steam. Switch off the gas and let the biryani stay covered for another 15 minutes.
Serve hot with Raita or salad.