Place half the butter in a saucepan and add the onion, cook gently over a low heat for 2-3 minutes without colouring. Then add the rice and turmeric and stir well.
Cook for another 2-3 minutes without colouring, and add twice the amount of stock to rice.
Season and cover with a lid, then bring to the boil and transfer in a covered oven -proof dish to a hot oven (230C) for approx. 15 minutes until cooked.
Remove immediately and transfer to a cold saucepan, carefully mix in the remaining butter, correct the seasoning and serve.