Wash potatoes; place in large saucepan. Cover with boiling water; bring back to boiling. Reduce heat; simmer, covered, 30 minutes, or until tender. Drain; let cool. Peel.
Preheat oven to 350°F.
Cut potatoes into ¼ inch thick slices. In 1½ quart shallow baking dish, layer potato slices alternately with orange slices.
In a small saucepan, combine brown sugar, cornstarch, salt, and spice. Gradually stir in orange juice; add butter. Bring to boiling over medium heat, stirring constantly. Boil gently 2 minutes. Pour over sweet potato and orange slices.
Bake, uncovered, 45 minutes or until hot and bubbly.
Yield: 6 servings