Scrub the potatoes, slice them, and put in a pot with water to cover. Boil the potatoes until tender, then drain and mash them with 2 tablespoons of the butter. Add the cottage cheese, onion, and salt and pepper to taste. Stir the mixture gently, and then put in a greased casserole. Dot with the remaining 2 tablespoons of butter and sprinkle with paprika. Bake, uncovered, for 30 minutes.