Drink beer with Frenchman in lone setting (6,5)
I believe the answer is:
bitter lemon
'drink' is the definition.
(bitter lemon is a kind of drink)
'beer with frenchman in lone setting' is the wordplay.
'beer' becomes 'bitter' (I've seen this before**).
'with' is a charade indicator (letters next to each other).
'frenchman' becomes 'm' (abbreviation for Monsieur - like 'Mr').
'in' is an insertion indicator.
'setting' indicates an anagram.
'lone' anagrammed gives 'leon'.
'm' placed into 'leon' is 'lemon'.
'bitter'+'lemon'='BITTER LEMON'
(Other definitions for bitter lemon that I've seen before include "Tart soft drink" , "Soft citrus drink" .)