Cook the rice in boiling salted water for approx. 20 mins. until just soft, drain, return to the pan, cover and keep warm.
Peel and finely chop the onion and garlic. Clean the mushrooms with a brush, cut the large mushrooms in half. Drain the tomatoes and cut into strips.
To cook the vegetables
Heat the butter in a non-stick frying pan. Briefly sauté the onion and garlic, add the mushrooms and tomatoes, cook for approx. 10 mins., season.
Mix the cornflour with the single cream and stock, add to the mushrooms. Bring the sauce to the boil, simmer for approx. 5 mins. while stirring occasionally, then season. Add the spinach, allow to wilt, serve with the rice.