Cut sweet potatoes in half crosswise. Cook in boiling water to cover 10 minutes. Drain and cool. Cut crosswise into 1/2" slices.
Combine brown sugar and next 3 ingredients in a medium saucepan. Bring to a boil; boil 10 minutes. Remove from heat; stir in vanilla.
Layer sweet potato and apple slices in a greased 13" x 9" baking dish. Pour glaze over slices. Bake, uncovered, at 400° for 1 hour or until potatoes are candied and glaze is thickened, basting with glaze after 30 minutes.