Cut flank steak into thin strips across the grain (flank steak is easier to cut if partially frozen) and toss the slices with 1/4 cup of flour.
Heat olive oil in a large skillet over medium heat; brown meat slices and onion in the hot oil. Stir in 2 tablespoons of flour, salt, pepper, and paprika. Add mustard, vinegar, tomato sauce and water; cover and simmer for 50 to 60 minutes, or until the beef is tender.
Serve with buttered noodles, potatoes, or rice.
Calories per serving: 469
Fat per serving: 24.9