Wrongly form pies to be cooked with mash (8)
I believe the answer is:
misshape
'wrongly form' is the definition.
'pies to be cooked with mash' is the wordplay.
'to be cooked with' indicates an anagram.
'pies' anagrammed with 'mash' can make 'MISSHAPE'.
(Other definitions for misshape that I've seen before include "How football appears to a rugby player" , "bad figure" , "Distort" , "Fashion poorly" , "Emphasis (anag.)" .)