Remove the pulp and seeds from the muscadines. Boil the hulls until tender in enough water to cover. Drain and reserve the juice, putting the hulls to the side. Mix together the sugar, cornstarch, vanilla and juice. Pour this mixture over the reserved hulls and let stand for 20 minutes. Pour the hulls and mixture into piecrust and dot with butter. Cover with lattice top and bake at 400 degrees for 15 minutes. Reduce heat to 375 degrees and bake for 45 minutes more.