Heat the corn oil in a large skillet over high heat.
Add the beef and sear on each side.
Place the beef in a warm plate. Add the onion to the skillet and sprinkle with paprika.
Mix the butter and onion and cook for 2 minutes. Add the mushrooms and reduce the heat to medium and cook for 2 minutes. Season to taste.
Pour the sauce over the ingredients, add the tomato sauce and the beef, and cook for about 10 minutes over low heat.
Add the sour cream before serving.
Serve with egg noodles and spinach.