Wash and pierce potatoes or yams. Place on a piece of heavy-duty foil and bake at 375°F for 40 to 50 minutes until just tender. Cool, peel and cut into 1-1/2 inch pieces. Spray 8 x 8-inch baking dish with nonstick cooking spray. Place cooked potatoes or yams in dish; set aside. In small pan, combine orange juice, agave, cornstarch, ginger, nutmeg and salt. Stir until smooth. Cook over medium-high heat stirring until thick and mixture begins to boil. Stir and cook for one minute. Remove from heat and stir in butter. Pour over potatoes or yams stirring to coat. Bake at 350°F for 25 to 30 minutes until hot and potatoes are tender.