Stir together sour cream and mustard; cover and refrigerate. Heat oven to 170 degrees F. Heat 12-inch skillet over medium-high. Coat beef with1 tablespoon oil; season with salt, pepper, and 1 teaspoon sugar. Brown in hot skillet 4 minutes,turning once. Transfer to platter; set aside.
Add remaining oil, carrots, and onion to skillet. Cook and stir 5 minutes, until browned. Add broth and potatoes; bring to boiling. Reduce heat; cook, covered, 15 minutes, until tender. Return beef to skillet. Simmer, covered, 8 minutes for medium (10 minutes for medium-well).
Reserving broth in skillet, transfer vegetables and beef to oven-safe platter; keep warm. Simmer broth; add spinach. Cook and toss with tongs 3 to 4 minutes.
To serve, ladle broth in bowls; reserve some to drizzle over meat and vegetables. Divide beef and vegetables among plates. Serve with mustard sauce. Makes 4 servings.
Salmon Boiled Dinner:Substitute four 6-ounce skinless salmon fillets for the steak. Omit oil and sugar and do not brown salmon, carrots, and onion. Simply bring broth, carrots, onion, and potatoes to boiling; reduce heat and simmer, covered, 15 minutes or until just tender. Season salmon with salt and pepper; add to vegetables and simmer, covered, for 5 to 8 minutes or until just cooked through. Continue with step 4. Once spinach has been added to platter, stir 1 tablespoon of lemon juice into the simmering broth; spoon some over each portion of salmon and vegetables. Serve with mustard sauce and lemon wedges.
Per Serving: cal. (kcal) 557, Fat, total (g) 27, chol. (mg) 111, sat. fat (g) 10, carb. (g) 35, Monosaturated fat (g) 9, Polyunsaturated fat (g) 6, fiber (g) 7, sugar (g) 8, pro. (g) 44, vit. A (IU) 20456, vit. C (mg) 47, Thiamin (mg) 0, Riboflavin (mg) 1, Niacin (mg) 11, Pyridoxine (Vit. B6) (mg) 1, Folate (µg) 274, Cobalamin (Vit. B12) (µg) 6, sodium (mg) 1269, Potassium (mg) 2069, calcium (mg) 202, iron (mg) 8, Percent Daily Values are based on a 2,000 calorie diet