Which he didn't...ever.
A long, literary detective story of the fake article that caused the hoax to be so persuasive - even to experts. Link: When Dickens met Dostoyevsky.
Do read it for its fabulous Borgesian twists and turns (whose works NF is currently devouring on his subway commutes). You will also be reminded of Benno von Archimboldi - the elusive fictional writer featured so prominently in Bolaño's 2666.
The meandering, somewhat long-winded article however, will appeal only to the literary minded and fans of either Dickens or Dostoyevsky or both. Be warned.