Things are going really well over at the Sterling Mason at 71 Laight Street, where 18 of its 32 apartments are in contract following the building’s July 2013 launch. Newly included in the jamboree, the building’s largest home, Penthouse B, which just went into contract for the full ask of $23 million, TRD reports. The six-bedroom, five-bathroom apartment is a 5,620-square-foot duplex that partially occupies its top two floors, and has three powder rooms, a fireplace, a 2,625-square-foot private terrace, library, and media room. The apartment’s sale price roughly translates to $4,004-per-square-foot, and although its the building’s most expensive apartment by price tag, Penthouse A has so far commanded the building’s most expensive price per …