Cook the rice in salted water for approx. 30 mins. until almost soft, drain. Return the rice to the pan, stir in the butter, cover and set aside.
Slice the mushrooms and chop the onion. Heat the butter, sauté the onion and mushrooms. Add the wine and reduce to half the volume.
Mix the cornflour with the single cream and bouillon, add to the pan, stirring, bring to the boil, cook for approx. 3 mins., and season. Serve the mushrooms with the rice. Finely chop the parsley and sprinkle over the top.