In a large saucepan, cook potatoes in boiling salted water until tender; drain. Mash the potatoes with butter, milk, salt, and pepper until smooth. Add cream cheese and onion dip; mix well. Spread in a greased 2-1/2 qt baking dish. Sprinkle with paprika. Cover and refrigerate for 8 hours or overnight. Remove from fridge 30 minutes before baking. Bake, uncovered, at 350 for 50-60 minutes or until heated through. Makes 12-14 servings.