Tenderize the steaks, salt them and sprinkle with black pepper. Arrange them in a tray and pour in a little oil. Bake at 392°F (200 °C) about 25-30 min.
Braise 1/2 of a finely chopped onion head in a pan. Add the mushrooms and after a few min. - the flour.
Stir, pour in the wine and about 2/3 cup (150 ml) water. Let it boil 10 min. and add the lightly beaten sour cream, salt and black pepper.
Stir and pour this over the steaks after 1 min. Return to the oven for 10 min. Serve the steaks with the sauce and mashed potatoes.