Notwithstanding any other provision of this article, where, before the expiration of the period prescribed for the assessment of a tax, a taxpayer has consented, in writing, that the period be extended, the amount of tax due may be assessed at any time within the extended period. The period so extended may be extended further by subsequent consents, in writing, made before the expiration of the extended period.
72 P.S. § 8213-A