Marinate the chicken with the ingredients mentioned under marination and set aside for at least 2 hrs and overnight is best.
Wash rice till the water runs clear. Soak for 20 to 30 minutes. Heat 2 ½ cups water in a utensil to cook rice. Add 1 tsp oil, dry spices and salt, let the water boil rapidly for 5 mins.
While the rice cooks, transfer the marinated chicken to a heavy bottom casserole, handi or non-stick. Add fried onions, green chilies, ½ of the mint, coriander leaves and pour in the oil or melted ghee. Mix well and level the surface.
Layer the cooked rice evenly, add fried onions, mint and coriander leaves over the chicken. Sprinkle ¼ tsp to ½ tsp. biryani masala powder.
Repeat steps of layering rice, coriander mint leaves and then fried onions. Pour the saffron milk all over.
Cover rim of the casserole with foil to trap the dum or use a cloth. Rinse a thick kitchen cloth and squeeze off the excess water, it must be just moist. Make a double layer. Spread this cloth over rim and cover lid over the casserole.
Place this over a thick hot tawa, set the flame to medium high such that the flame reaches all over the diameter of the casserole. Cook this way for exactly 20 mins. After 20 mins, if you have a see thru lid you can see the vapour filled.
Now reduce the flame to min (as low as in Indian stoves or burners, where the flame barely touches tawa). Cook this way for exactly 10 to 15 mins. You can see the vapour dripping on the moist cloth.
Turn off the flame and leave it as it is for at least 20 to 30 mins. Garnish chicken biryani and serve.