Heat oven to 350 degrees.
Butter a shallow baking dish, about 13 X 9 1/2 X 2 inches.
Combine potatoes, onions, parsley, salt and pepper.
Spread evenly in prepared pan.
Dot with butter.
Pour boiling water over all.
Bake about 1 hour and 15 minutes or until water is absorbed but potatoes are moist and tender and well browned on top.