Food for the morning in Borstal is cooked (5,4)
I believe the answer is:
roast lamb
'food' is the definition.
(roast lamb is a kind of food)
'the morning in borstal is cooked' is the wordplay.
'the morning' becomes 'am'.
'in' is an insertion indicator.
'is cooked' indicates an anagram.
'borstal' with letters rearranged gives 'roastlb'.
'am' going into 'roastlb' is 'ROAST LAMB'.
'for' acts as a link.
(Other definitions for roast lamb that I've seen before include "cut at the weekend" , "Dish with mint sauce" , "Something to eat" .)