Lightly toast the saffron strands in a dry pan until fragrant. Soak the saffron in the warmed milk and set aside to infuse. This step enhances the aroma and adds a subtle golden hue to the rice.

Heat the oil in a deep frying pan. Add the sliced onions and fry until they turn dark golden brown and crispy. Stir frequently to avoid burning. Once fried, remove the onions and drain on a paper towel. Set aside one-third of the onions for the chicken marinade and reserve the remaining for assembly.

In a large mixing bowl, combine the yogurt, ginger paste, garlic paste, green chili paste (if using), red chili powder, turmeric, coriander powder, cumin powder, garam masala, salt, pepper, lemon juice, and one-third of the fried onions. Add the chicken pieces and coat thoroughly. Cover and marinate for at least 30 minutes, preferably up to 3 hours for deeper flavor.

Transfer the marinated chicken to a heavy-bottomed pot. Cover and cook over medium-low heat for approximately 15 minutes, or until the chicken is mostly cooked through. Add ½ cup of water to loosen the sauce if necessary.

In a large pot, bring 2-3 liters of water to a boil. Add salt, oil, black and green cardamom pods, cloves, bay leaves, and the cinnamon stick. Add the basmati rice and boil until it is about 50% cooked (grains should be soft on the outside but firm inside), roughly 10 minutes. Drain the rice and spread it out on a flat surface or tray to cool slightly.

In a large, heavy-bottomed pot, begin by layering half of the cooked chicken at the bottom. Spread a layer of partially cooked rice over the chicken. Sprinkle with fresh coriander, mint leaves, fried onions, a drizzle of saffron milk, and ghee. Repeat the layers with the remaining chicken and rice, finishing with rice on top. Optionally, sprinkle the biryani coloring over the top for visual appeal.

Cover the pot tightly with two layers of aluminum foil and place a lid over it to seal. Bake in a preheated oven at 200°C (390°F) for 20 minutes. Lower the temperature to 180°C (350°F) and continue baking for an additional 45 minutes. This slow-cooking process allows the flavors to meld together.

Once cooked, remove the biryani from the oven and let it rest, covered, for 10 minutes before serving. Using a flat spatula, gently scoop from the bottom to ensure all layers are served. Garnish with remaining fried onions and fresh coriander.