As a rule, veg is cooked for this dish (5,7)
I believe the answer is:
liver sausage
'this dish' is the definition.
(type of food)
'as a rule veg is cooked' is the wordplay.
'cooked' is an anagram indicator.
'as'+'a'+'rule'+'veg'+'is'='asarulevegis'
'asarulevegis' is an anagram of 'LIVER SAUSAGE'.
'for' is the link.
(Other definitions for liver sausage that I've seen before include "deli purchase" , "savoury spread" , "savoury paste" , "Rolled meat paste" .)