1. Remove the core from each kidney and cut in half. Dredge with seasoned flour.
2. Heat the butter and gently cook the onion on a low heat. Remove from the pan into an ovenproof dish.
3. Saute the kidneys for a few minutes on either side until golden brown.
4. Add mushrooms and continue cooking for about 2 minutes.
5. Add the tomatoes and red wine.
6. Spoon into the ovenproof dish, cover with foil and bake for 25 minutes at 180°C (350°F) Gas 4.
7. Serve individual portions in a ring of rice on the plate and garnish with parsley.