Cook potatoes in boiling water 20 min. or just until tender; drain. Return to pan; cover with cold water. Let stand until cooled.
Meanwhile, melt butter in medium saucepan on medium heat. Add onions; cook and stir 2 min. Blend in flour; cook 1 min. Gradually add milk; cook 5 min. or until thickened, stirring constantly. Add 1-1/4 cups mozzarella; cook and stir 1 min. or until melted. Stir in mustard.
Heat oven to 375°F. Peel potatoes; cut into 1/4-inch-thick slices. Layer alternately with cheese sauce in 2-qt. casserole sprayed with cooking spray, ending with sauce.
Bake 25 to 30 min. or until heated through. Top with remaining cheeses; bake 5 min. or until mozzarella is melted.
Serve this tasty potato side dish with a mixed green salad or hot steamed vegetable, and a serving of cooked lean meat, poultry or fish.
Calories From Fat
% Daily Value*
Total Fat 10g
Saturated Fat 6g
Trans Fat 0g
Total Carbohydrates 23g
Dietary Fibers 2g
* Percent Daily Values are based on a 2,000 calorie diet.
* Nutrition information is estimated based on the ingredients and cooking instructions as described in each recipe and is intended to be used for informational purposes only. Please note that nutrition details may vary based on methods of preparation, origin and freshness of ingredients used.