N.Y. State Fin. Law § 157

§ 157. Release of part of mortgaged premises. If the owner of\nmortgaged premises sell a part thereof, the comptroller, on application\nand with the consent of the mortgagor or such owner may release the part\nof the mortgaged premises sold from the lien of the mortgage. Such\nrelease, however, shall not be given unless a sum approved by the\ncomptroller shall be first paid upon the mortgage and unless the part of\nthe mortgaged premises remaining unsold, exclusive of buildings and\nprior liens, is worth double the residue of the mortgage debt. The\ncomptroller shall execute such release in the usual form, which, when\nacknowledged, shall be recorded by the county clerk and a minute thereof\nmade upon a margin of the mortgage.\n