In the case of a plot of land for which a plan for the subdivision of which into two or more parcels or lots for the purpose of development and sale has, prior to the effective date of this chapter, been duly approved and recorded as required by law, which plan does not make provision for full adherence to the regulations of this chapter governing minimum lot areas or widths, front, side or rear yards or building coverage but was in conformity with regulations as were effective at the time such plan was approved and recorded, the development and sale contemplated by the plan may be proceeded with when authorized as a variance or if the subdivision approval was secured within one year of the effective date of this chapter. The Zoning Hearing Board shall have the power to grant a variance with respect to the whole of such plot of land or any portion thereof.