Peel and finely dice the onion. Heat the butter in a saucepan and fry the onions until translucent. Add rice and turmeric powder and sauté briefly. Salt the rice and add 300 ml of water. Cover and bring to the boil and cook over a low heat for about 20 minutes.
In the meantime, roughly chop the cashew nuts. Pour off any remaining liquid from the rice. Mix in the cashew nuts and serve immediately.