Cook potatoes in salted water until tender; drain. Beat potatoes, milk, seasoned salt and 2 tablespoons butter in a mixing bowl until fluffy. Mix in sour cream, cream cheese and chives. Pour into greased 13"x9" baking pan. Combine remaining one tablespoon of butter with crushed cracker crumbs; sprinkle on top of potato mixture. Bake, uncovered, at 350 degrees for 30 minutes. Top with shredded cheese during last 10 minutes of baking time.