To cook basmati rice separately:-Soak basmati rice in water for about 10 minutes. Wash the rice gently ensuring to take out only starch and not break the grains. Mean while add about 4 liters of water in a large vessel and bring it to boil. Once water starts to boil, add about 1 teaspoon of cooking oil and 1 teaspoon of salt. Add the soaked and washed rice, stir gently once and cook for about 3 to 5 minutes(I usually take it off heat by 3 ½ minutes). Keep an eye on rice as some brands of basmati rice cooks very fast and some takes time. My rice was cooked in 5 minutes. Drain the water immediately and spread the rice on a large plate.
Clean and wash the chicken thoroughly for at least 3 times. Add a little salt while washing the chicken(this will help to get rid off the smell to an extent)
Marinate the chicken with ingredients mentioned under marinating list. Marinate for at least ½ hour.
In a deep bottomed pan add oil, once oil gets heated add 1 onion slices and fry it until brown (don’t burn the onions). Remove browned onion from oil and keep it aside. This will be used for garnishing and will making the layers.
To the same pan add remaining onions(2 onions) slices and saute till onions turn translucent. Next add ginger-garlic paste and saute till the raw smell goes off.
Add slit green chilies and mix for a minute. Add chopped tomatoes and saute till tomatoes turn slightly mushy. Next add red chili powder, coriander powder, garam masala powder and salt(to taste, remember chicken marinate contains salt as well). Saute for 2 minutes.
Add 3 tbspns of both coriander and mint leaves and mix. Add marinated chicken and mix well. Cook until chicken is fully cooked(chicken pieces should be very tough, if you pull the chicken flesh, it should come off from bones). DO NOT add any water as onion tomato gravy and the chicken marination (as we have used curd) will release enough water. Once chicken is cooked if you find there is excess water remove the water from the gravy and keep it aside. You can use this gravy water while layering and also can serve this with biryani along with raita. The gravy water will taste very close to “salna”.
Take the Dum pan, add ghee and spread it to coat all the bottom and sides of the pan, reduce the flame to low. Add about 2 full tbspns of the chicken gravy(remember it shouldn’t be very watery) spread all over the bottom. Next add cooked basmati rice over the chicken and gently spread the rice to cover the chicken. At this stage you can use the watery gravy that you removed in step 6. Use a tea spoon and remove the top oily layer from gravy and drizzle over the rice, this will add flavors to the rice and also give color or you can add colors(saffron soaked in milk and orange food color)
Repeat step 7 until you have used up all rice and chicken. Over the top sprinkle coriander and mint leaves and browned onions and close with a lid. Ensure the flame is low and place a heavy weight on top of lid to trap the steam inside. Leave it alone for 10 minutes and your dum biryani is ready.
Scoop out biryani from the edges of the pan, making sure not to break the rice grains. Serve hot with onion raita.