Place potatoes in a Dutch oven or large kettle; cover with water and bring to a boil. Reduce heat; cover and cook for 20-25 minutes or until potatoes are tender. Drain and place in a bowl; mash. Add sour cream, cream cheese, 4 tbsp butter, onion and salt; stir until smooth and the cream cheese and butter are melted. Spread in a greased 13x9x2-inch baking dish. Melt remaining butter; drizzle over potatoes. Sprinkle with paprika. Refrigerate or bake immedately, covered, at 350° for 40 minutes; uncover and bake 20 minutes longer. If potatoes are made ahead and refrigerated, let stand at room temperature for 30 minutes before baking.