Author, autobiographical at heart, penning worthiest novel (11)
I believe the answer is:
Here is my best explanation:
'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'.