A measure of gin or a Campari served up for old dandy (8)
I believe the answer is:
macaroni
'for old dandy' is the definition.
(I've seen this before)
'a measure of gin or a campari served up' is the wordplay.
'a measure of' says the answer is hidden in the clue (a portion or measure of the clue).
'served up' says the letters should be written backwards (in a down clue, letters go up).
'inoracam' is hidden within 'gin or a campari'.
'inoracam' back-to-front is 'MACARONI'.
(Other definitions for macaroni that I've seen before include "Long thin pasta" , "Slender tubes of pasta" , "Cora and Mina go for pasta" , "sort of pasta" , "Tubular pasta" .)