Peel and slice potatoes about 1 inch thick. Arrange in lightly greased 1 1/2 quart casserole dish.
In small saucepan, stir together sugar, cornstarch, salt and orange peel.
Slowly stir orange juice into the sugar mixture.
Add butter. Cook stirring constantly until mixture boils and thickens. Boil and stir about 1 minute.
Pour hot orange sauce over sweet potatoes. Cover and bake 1 hour, basting occasionally.
Note: During Christmas I often bake the potatoes and prepare the sauce ahead of time. I then reheat the sauce, assemble and bake for about 30 minutes at 350F until heated through. Can be topped with marshmallows if desired.