Combine first 3 ingredients. Dredge cubed steak in flour mixture. Brown steak, in batches, in hot oil in a Dutch oven. Stir in tomato sauce and soup mix; bring to a boil. Cover, reduce heat and simmer 15 minutes. Remove steak, reserving liquid in pan; keep warm. Stir sour cream into tomato mixture; simmer, stirring constantly, until heated. Serve over steak.