1/2 cup LAND O LAKES® Sour Cream
2 tablespoons fat free skim milk
1 tablespoon prepared horseradish
1 tablespoon country-style Dijon mustard
8 ounces deli Italian roast beef, cut into 1/8-inch strips
1/2 cup sliced red onion, separated into rings
2 Roma tomatoes, sliced 1/4-inch
6 cups torn fresh spinach
Stir together all dressing ingredients in medium bowl; set aside.
Spray 12-inch skillet with no stick cooking spray; add beef and onions.
Cook over medium heat, stirring occasionally, until onions just begin to soften and beef is heated through (2 to 3 minutes).
Toss together beef mixture, spinach, tomatoes and dressing in large bowl.
If desired, serve with croutons or garlic toast.