In a large pot, heat water to a boil. Cut peeled sweet potatoes in half and add to the pot. Cook for 10 minutes, and then let cool down enough to handle.
Meanwhile, core apples and slice into ½" rings.
Once sweet potatoes or yams have cooled down, slice them into ½" rings.
Preheat oven to 400 degrees.
Melt butter in a saucepan and add brown sugar, apple cider, and salt. Cook for 5-8 minutes, until sauce thickens. Add vanilla and remove from the heat.
Layer sweet potatoes and apple slices in a greased 9" x 13" baking dish. Pour the cooked glaze evenly over them.
Bake uncovered for one hour. After 30 minutes, bast glaze and return to oven for 30 minutes more.
