Slice beef across the grain into very thin strips.

Heat 1 tablespoon of margarine in a skillet over high heat.

Cook half of the beef and chopped onion until the beef is no longer pink and the onion is tender.

Set the cooked beef and onion aside.

Repeat the cooking process with the remaining beef, margarine, and chopped onion.

Return all of the cooked beef and onion mixture to the skillet.

Stir in the undiluted cream of mushroom soup and paprika.

Heat the mixture through, ensuring it is well combined.

Stir in the sour cream until fully incorporated.

Serve the Beef Stroganoff hot over cooked noodles or rice.