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-quart casserole; dot with butter and sprinkle with paprika.
If made ahead, cover and refrigerate until the next day.
Bake, covered, in a 400 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.