Cook sweet potatoes in boiling water 10 minutes; let cool to touch. Peel and cut into 1/4-inchthick slices; set aside.
Roll half of pastry to 1/8-inch thickness on a lightly floured surface. Carefully fit into a 9- inch pie plate. Chill remaining pastry. Arrange sweet potato slices evenly in the pastry shell, and set aside.
Combine sugar, water, butter, and spices; stir well. Pour mixture over sweet potatoes.
Roll out remaining pastry to 1/8-inch thickness on a lightly floured surface, and place over filling. Trim edges; seal and flute. Cut slits in top pastry to allow steam to escape. Bake at 325° for 50 minutes or until golden brown. Cool pie before serving.