Grease a 13x9-inch glass baking dish with butter or margarine. Boil yams whole in a pot of boiling water for 30 minutes. Set aside to cool.
Peel and slice yams lengthwise and spread out along bottom of baking dish. Peel and slice apples and place on top of yams. After removing the seeds, squeeze juice of orange over yams. Add walnuts evenly over yams.
Crumble brown sugar and pour honey over yams. Dot yams with 2 tablespoons butter or margarine. Top with marshmallows.
Bake, uncovered, at 350 degrees for about 1 hour. Marshmallows will be lightly browned and melted.
Note:"This dish can be made one day in advance and re-heated on Thanksgiving."