Having drunk beer, cook a light vegetable (5,9)
I believe the answer is:
globe artichoke
'vegetable' is the definition.
(globe artichoke is a kind of vegetable)
'having drunk beer cook a light' is the wordplay.
'having drunk' indicates anagramming the letters (I've seen 'have drunk' mean this (I've seen this in other clues)).
'beer'+'cook'+'a'+'light'='beercookalight'
'beercookalight' anagrammed gives 'GLOBE ARTICHOKE'.
(Other definitions for globe artichoke that I've seen before include "Flower head used as vegetable" , "plant" , "Blooming head" .)