Preheat oven to 350°. Place potatoes in a Dutch oven; add water to cover. Bring to a boil. Reduce heat; cook, uncovered, until tender, 8-12 minutes. Drain. Cool slightly., In a large bowl, mix soup, onion dip, milk, sour cream, parsley, salt and pepper; gently fold in potatoes and cheese. Transfer to a greased 13x9-in. baking dish., Bake, covered, 30 minutes. Uncover; bake until heated through and cheese is melted, 15-20 minutes longer. Just before serving, stir to combine; sprinkle with additional parsley. (Potatoes will thicken upon standing.)