Arrange yams in a lightly greased 13" x 9" baking dish. Sprinkle brown sugar over yams. Combine butter and next 2 ingredients. Drizzle over yams. Bake, uncovered, at 425° for 20 minutes. Sprinkle marshmallows over yams, if desired, and bake 5 more minutes. Let stand 10 minutes before serving.