Grind the special garam masala ingredients into a fine powder and set it aside.
Marinate the chicken with all the listed ingredients and allow it to rest for at least two hours, though overnight is ideal.
Wash the basmati rice thoroughly three to four times and let it soak for 30 minutes.
Heat oil in the pot you will use for assembling the biryani, fry the onions until golden, then drain and set them aside, keeping the flavored oil.
Soak saffron in warm milk while separately heating ghee in a saucepan to fry cashews and sultanas until golden, reserving them for garnishing.
Bring a large pot of salted water to a boil, then add the drained rice and cook for five to seven minutes until it is half-cooked but still has a bite.
In the same pot used for frying onions, add the reserved oil and cook the marinated chicken, mixing well.
Layer the partially cooked rice over the chicken, then top with fried onions, chopped herbs, saffron milk, fried nuts with ghee, and a few drops of kewra and rose essence.
Cover the pot tightly with foil and a heavy lid, then place a weight on top to trap steam, allowing it to cook on a very low flame for 30 to 35 minutes.
Turn off the heat and let the biryani rest for 10 minutes before removing the lid and carefully fluffing the rice with the back of a ladle.
Serve hot with raita.