Place potatoes in a large kettle; cover with water. Add 1/2 teaspoon salt; cook until tender. Drain; mash potatoes until smooth. In a large saucepan, cook and stir the butter, cheese, milk and remaining salt until smooth. Stir into potatoes; fold in eggs. Pour into a greased 3-quart baking dish. Bake, uncovered, at 350° for 40 minutes or until puffy and golden brown. Sprinkle with chives if desired.