Preheat oven to 350°. Place potatoes in a 6-qt. stockpot; add water to cover. Bring to a boil. Reduce heat to medium; cook, uncovered, until tender, 10-15 minutes. Drain; transfer to a large bowl. , Add butter, sour cream, salt and pepper; beat until blended. Beat in whipping cream. Stir in cheeses and chives. , Bake, covered, 45 minutes, stirring after 30 minutes. Sprinkle with toppings; bake, uncovered, until heated through, about 15 minutes.