Seafood best cooked in liquid, or roasted to begin with (7)
I believe the answer is:
lobster
'seafood' is the definition.
(lobster is a kind of seafood)
'best cooked in liquid or roasted to begin with' is the wordplay.
'cooked' is an anagram indicator.
'in' is an insertion indicator.
'to begin with' indicates taking the first letters.
The first letters of 'liquid or roasted' is 'lor'.
'best' with letters rearranged gives 'bste'.
'bste' inserted into 'lor' is 'LOBSTER'.
(Other definitions for lobster that I've seen before include "Large marine crustacean" , "Large edible crustacean" , "Lets bro have the shellfish" , "Crustacean with pincer-like claws" , "food?" .)