Tea in a quantity to be served up (5)
I believe the answer is:
assam
'tea' is the definition.
(I've seen this before)
'a quantity to be served up' is the wordplay.
'quantity' becomes 'mass' (mass is a kind of quantity).
'to be served up' says the letters should be written backwards (in a down clue, going upwards).
'mass' reversed gives 'ssam'.
'a'+'ssam'='ASSAM'
'in' is the link.
(Other definitions for assam that I've seen before include "region out east" , "Indian state, famed for its tea" , "place associated with tea" , "Indian province" , "North-east Indian tea state" .)