Marinate the Chicken: In a large mixing bowl, combine the chicken pieces with all the marinade ingredients: yoghurt, ginger-garlic paste, turmeric, chilli powder, ground coriander, garam masala, lemon juice, and salt. Mix thoroughly to ensure every piece is well-coated. Cover and refrigerate for at least 1 hour, or ideally overnight for the most flavorful chicken.

Prepare the Rice: Rinse the basmati rice in cold water until the water runs clear. Soak the rice in fresh cold water for 30 minutes. While it soaks, bring a large pot of water to a rolling boil and add the 2 tbsp of salt, cinnamon stick, cardamom pods, cloves, and bay leaf.

Par-Cook the Rice: Drain the soaked rice and add it to the boiling water. Cook for 5-7 minutes, until the rice is about 70% cooked—it should still have a slight bite. Immediately drain the rice in a colander and set it aside, leaving the whole spices in.

Fry the Onions (Birista): While the rice cooks, heat the ghee or oil in a large, heavy-bottomed pot or Dutch oven over a medium heat. Add the thinly sliced onions and fry for 15-20 minutes, stirring often, until they are deep golden brown and crispy. I find that consistent stirring towards the end prevents them from burning. Remove half of the onions with a slotted spoon and set them aside on a paper towel for garnish.

Cook the Chicken: Add the marinated chicken to the pot with the remaining onions. Cook over a medium-high heat for 10-12 minutes, stirring occasionally, until the chicken is sealed and the gravy has thickened slightly. It doesn't need to be fully cooked through at this stage.

Layer the Biryani: Turn the heat down to low. Sprinkle half of the chopped mint, coriander, and reserved fried onions over the chicken. Gently spoon the drained, par-cooked rice over the chicken in an even layer.

Add the Final Flavours: Soak the saffron threads in the warm milk for a few minutes. Drizzle the saffron milk over the top of the rice. Scatter the remaining mint, coriander, fried onions, and the green chillies (if using) over the rice.

'Dum' Cooking: Cover the pot with a layer of foil and then place the lid on tightly to create a good seal. This is the crucial 'dum' technique which traps the steam. Cook on the lowest possible heat for 20-25 minutes.

Rest and Serve: Turn off the heat and let the biryani rest, still sealed, for at least 10 minutes. This allows the flavours to settle and the rice to finish cooking. To serve, gently fluff the rice with a fork and serve hot, ensuring you get a good mix of the rice and the chicken masala from the bottom.