Wine’s harsh — ultimately, trouble with gold filling (8)
I believe the answer is:
sauterne
'wine's' is the definition.
(Sauterne is an example)
'with gold filling' is the wordplay.
'with' is an insertion indicator.
'gold' becomes 'Au' (Au is the chemical symbol for gold).
'filling' becomes 'sterne' (I can't justify this - if you can you should give a lot more credence to this answer).
'au' going into 'sterne' is 'SAUTERNE'.
'harsh ultimately trouble' acts as a link.
This may not be right. Some or all of it may belong to another bit of the clue.
Can you help me to learn more?
(Other definitions for sauterne that I've seen before include "Sweet French white wine" , "Sweet white wine from around Bordeaux" , "Sweet white dessert wine" , "drink" , "Golden dessert wine, US style" .)