Heat the oil in a large saucepan and add the onion, carrot and celery, then cook gently until softened. Add the sugar and vinegar, cook for 1 min, then stir through the tomato purée. Add the chopped tomatoes or passata, the vegetable stock, and any brown rice, if using, then cover and simmer for 10 mins. If you are using wild rice, add this and simmer for 10 mins more. Finally, add any white rice you’re using, and simmer for a final 10 mins until the rice is tender.