Best drink concerned with this writer (7)
I believe the answer is:
supreme
'best' is the definition.
(I've seen this before)
'drink concerned with this writer' is the wordplay.
'drink' becomes 'sup' (I've seen this before).
'concerned with' becomes 're'.
'this writer' becomes 'me' (the person who is writing these clues).
'sup'+'re'+'me'='SUPREME'
(Other definitions for supreme that I've seen before include "Greatest in status, authority or power" , "Unrivalled" , "God" , "Most excellent" , "Cardinal, foremost" .)