Place yams in a large saucepan with enough water to cover. Bring to a boil, and cook 30 minutes, or until tender but firm. Drain, peel, and cut into 1/3 inch thick slices.
Preheat oven to 375 degrees F (190 degrees C). Lightly grease a 9x13 inch baking dish.
In a small saucepan over medium heat, melt the butter with the cornstarch and brown sugar. Mix in the apple juice, lemon juice, cinnamon, and allspice.
Alternate layers of yams and apples in the prepared baking dish. Pour the apple juice mixture over the layers.
Cover, and bake 1 hour in the preheated oven. Remove cover, and continue baking 30 minutes. Baste frequently with the juices from the pan to prevent drying.
