Sire cooked, then expected leftovers (7)
I believe the answer is:
residue
'leftovers' is the definition.
(I've seen this in another clue)
'sire cooked then expected' is the wordplay.
'cooked' indicates anagramming the letters (letters cooked into a new form).
'then' says to put letters next to each other.
'expected' becomes 'due' (similar in meaning).
'sire' anagrammed gives 'resi'.
'resi'+'due'='RESIDUE'
(Other definitions for residue that I've seen before include "Lees, dregs" , "balance" , "Remains to be seen" , "Something left over" , "Net worth of estate" .)