A bitter mixture goes to the priest's head (7)
I believe the answer is:
biretta
'the priest's head' is the definition.
The definition and answer can be both man-made objects as well as being singular nouns.
Perhaps there's a link between them I don't understand?
'a bitter mixture' is the wordplay.
'mixture' is an anagram indicator.
'a'+'bitter'='abitter'
'abitter' is an anagram of 'BIRETTA'.
'goes to' is the link.
Can you help me to learn more?
(Other definitions for biretta that I've seen before include "Cloth cap" , "religious headwear" , "Square cap worn by Roman Catholic clergy" , "that covers a Catholic priest" , "Cleric takes this on himself" .)