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.