In a large saucepan cook potatoes in boiling salted water until tender. Drain. Over low heat shake pan to dry potatoes. Keep warm.
Preheat oven to 375 degrees. Heavily butter a 2 1/2 quart casserole. In a large mixer bowl beat together cream cheese and sour cream until smooth. While beating add potatoes, one at a time. Add green onions, bacon and salt and pepper to taste; mix well. Pour into dish. (Casserole potatoes can be prepared to this point and refrigerated. Bake for 30-40 minutes.)
Drizzle with butter or margarine. Bake for 20-25 minutes or until heated through.
Serve hot, sprinkled with parsley.