The judge of an essayist? (5)
I believe the answer is:
trier
I believe this clue is a double definition.
'the judge' is the first definition.
(trier is a kind of judge)
'an essayist?' is the second definition.
'of' is the link.
(Other definitions for trier that I've seen before include "Persistent type" , "One has a crack" , "One wouldn't give up" , "Tester, juror" , "Judge, say" .)