Place potatoes in a large stockpot. Cover with water and add ½ teaspoon salt to water. Bring to a boil, reduce heat to simmer and cook until potatoes are tender, about 15 minutes. Drain and return to the stockpot.
Add sour cream, cream cheese, 2 tablespoons butter, milk, salt and pepper to potatoes and beat with an electric hand mixer until smooth. Spread into a greased 13x9-inch baking dish. Cover and store in the refrigerator until ready to bake (up to 2 days).
When ready to bake, brush top with 1 tablespoon melted butter and sprinkle with paprika.
Bake, uncovered, in a preheated 350°F oven 30 minutes or until bubbly.