Assemble recipe as directed, except do not top with remaining cheese. Refrigerate up to 24 hours. When ready to serve, bake, uncovered, 50 min. or until heated through. Top with remaining cheese; bake 5 min. or until melted.
This is a great way to use leftover mashed potatoes. Just prepare as directed, substituting 2-1/2 cups leftover mashed potatoes for the container of refrigerated mashed potatoes.
Prepare using refrigerated sour cream-and onion-flavored mashed potatoes.