You can add strands of saffron in kewra/ screw pine water . Add it in dots on the rice. Garnish with remaining coriander leaves, 1 TBSP of kasoori methi and the fried onions.
If putting it in the oven, let the oven heat up to 300F and leave it in for 40-50 mins.
If on gas, let it dumm on high flame for 5 mins and then on low-medium for another 30 mins. Try to keep the biryani pot on a tawa so it does not come in direct contact with the flame.