In a bowl, stir together cream cheese, garlic salt, pepper, and sour cream; set aside. Prepare and boil quartered potatoes; drain. Using an electric mixer or a potato masher, beat hot potatoes until they're in fine lumps. Add sour cream mixture and continue beating until smooth. Spoon potatoes into a well buttered 2 litre casserole; dot with butter and sprinkle with paprika. If made ahead, cover and refrigerate until the next day. Bake, covered, in a 400 deg F oven for 25 minutes (50 minutes if refrigerated); uncover and bake for 10 minutes more or until top is golden brown. Garnish with parsley sprigs, if desired. Makes 6 servings.