In a large saucepan, cook potatoes in boiling water until done. Drain and place in a greased 2-1/2-qt. baking dish. In a saucepan, melt butter. Add the flour, salt and pepper; stir to form a smooth paste. Gradually add milk, stirring constantly. Bring to a boil; boil and stir for 1 minute. Add cheese; stir just until melted. Pour over potatoes. Cover and bake at 350° for 45-50 minutes or until bubbly. Sprinkle with parsley.