Mashed Potato, Cream Cheese and Chive Gratin

Preheat oven to 375 degrees. Butter a 6 to 8 cup baking dish. Cook potatoes in boiling salted water until tender, about 12 to 15 minutes. Drain potatoes and return to pot. Add cream cheese and mash. Add sour cream, milk, chives, salt and pepper. Transfer mixture to prepared dish and dot top with butter. Bake about 30 minutes until potatoes are heated through and top is lightly browned. Let stand 5 minutes before serving.