Heat the oven to 190°C fan.
Add the chicken, rice, cauliflower, onion, tomatoes, tomato purée, garlic, biryani seasoning and butter, if using, to a large shallow casserole dish.
Pour over the hot chicken stock and mix well, making sure the rice is evenly distributed and sitting in the liquid.
Cover tightly and bake for 1 hour to 1 hour 15 minutes, checking towards the end.
It’s ready when the brown rice is tender and the chicken is cooked through.
Top with coriander if you fancy it.
