Place potatoes in a Dutch oven and cover with water. Bring to a boil. Reduce heat; cover and cook for 10-15 minutes or until tender. Drain; mash potatoes with cream cheese, sour cream and butter. Stir in milk and seasonings.
Transfer potato mixture to a greased 13-in. x 9-in. baking dish; sprinkle with cheese, onions and bacon. Cover and refrigerate until ready to use
Remove from the refrigerator 30 minutes before baking. Bake, uncovered, at 350° for 40-50 minutes or until heated through