Twain was referring to ANNE OF GREEN GABLES.  I have the quote in
a secondary source:  The Dial, February 1986.  It is the PBS guide
that just happened to be promoting both ANNE and the four-hour
HUCK FINN remake.

Clemens sent a copy of the book to Frances Nunnally in October
of 1908.  See Gribben's MARK TWAIN's LIBRARY: A RECONSTRUCTION,
vol. I, pg. 480.  In a letter to Francis Wilson, Clemens
states "In 'Anne of Green Gables' you will find the dearest
and most delightful child since the immortal Alice."

KB