Author, autobiographical at heart, penning worthiest novel (11)
I believe the answer is:
ghostwriter
'author' is the definition.
(ghostwriter is a kind of author)
'autobiographical at heart penning worthiest novel' is the wordplay.
'at heart' indicates the central letters.
'penning' indicates putting letters inside.
'novel' indicates an anagram.
The centre of 'autobiographical' is 'gr'.
'worthiest' anagrammed gives 'hostwrite'.
'gr' placed around 'hostwrite' is 'GHOSTWRITER'.
(Other definitions for ghostwriter that I've seen before include "Author denied credit" , "Maybe Sheridan Le Fanu" , "scibe for the incapable" , "second involved in an autobiography?" .)