Begin by preparing the chicken. Cut it into evenly sized pieces and place in a bowl with the ginger–garlic paste, turmeric, coriander, chilli powder, and a generous pinch of salt. Turn the pieces until well coated, then cover and leave to marinate for at least 30 minutes, or up to an hour. This allows the spices to gently permeate the meat, ensuring both tenderness and depth of flavour.
Meanwhile, rinse the basmati rice until the water runs clear, then leave it to soak for around 30 minutes. Bring a large pot of water to a vigorous boil and season generously with salt. Add the mint leaves, a portion of the whole spices, and a drizzle of oil. Drain the rice and add it to the pot, cooking until the grains are just tender on the outside while still retaining a slight firmness within. Drain carefully and set aside—the rice should remain long, separate, and lightly perfumed.
Preheat the air fryer to 200°C and lightly oil the rack. Arrange the marinated chicken in a single layer, ensuring there is space between each piece. Cook briefly until the exterior is set and lightly coloured, but not fully cooked through. This stage preserves the chicken’s succulence as it finishes later within the biryani.
For the masala base, blend the onion, tomatoes, ginger–garlic paste, and cashews into a smooth, velvety purée. In a heavy pot or clay vessel, melt the butter and add the cumin seeds and remaining whole spices, allowing them to release their aroma. Stir in the blended mixture and cook slowly until it deepens in colour and the butter begins to separate, signalling that the base has developed richness and depth. Finish by stirring through the kasuri methi.
Add the partially cooked chicken to the masala, turning gently to coat each piece. Fold in the yogurt, loosening with a splash of water if needed, and allow the mixture to simmer briefly so the flavours begin to meld. Taste and adjust the seasoning at this stage.
To assemble, spoon the prepared rice evenly over the chicken, allowing it to settle naturally without pressing. Lightly dust with garam masala, then scatter over the fresh herbs and crisp fried onions. Cover with a tight-fitting lid and cook over a steady heat—beginning on a slightly higher flame before reducing to low—allowing the biryani to steam and the layers to come together.
Once cooked, remove from the heat and leave to rest, undisturbed, for several minutes. Just before serving, gently fluff the rice, lifting from the base to reveal the richly spiced chicken beneath. Serve warm, with raita or your chosen accompaniments, allowing the aroma to rise as it reaches the table—deep, fragrant, and quietly indulgent.
