Mint tea without sugar, the ultimate posh drink (9)
I believe the answer is:
cointreau
'drink' is the definition.
(I've seen this before)
'mint tea without sugar the ultimate posh' is the wordplay.
'mint' becomes 'coin' (synonyms).
'without' indicates putting letters inside ('without' can be similar in meaning to 'outside').
'the ultimate' indicates one should take the final letters.
'posh' becomes 'u' (abbreviation for upper-class - opposite to non-u).
The final letter of 'sugar' is 'r'.
'tea' placed around 'r' is 'trea'.
'coin'+'trea'+'u'='COINTREAU'
(Other definitions for cointreau that I've seen before include "Orange liqueur" , "A sweet orange-flavoured liqueur for cautioner" , "Sweet orange-flavoured colourless liqueur" , "Alcoholic drink" .)