In auditorium, performer serves Heather cocktail (9,5)
I believe the answer is:
singapore sling
'cocktail' is the definition.
(I've seen this before)
'in auditorium performer serves heather' is the wordplay.
I cannot really see how this works, but
'in' is found in the answer.
'heather' could be 'ling' (synonyms) and 'ling' is found within the answer.
This explanation may well be incorrect...
Can you help me to learn more?
(Other definitions for singapore sling that I've seen before include "Drink" , "Type of cocktail" .)