Top off cook (5)
I believe the answer is:
outdo
'top' is the definition.
(both can mean to surpass or beat)
'off cook' is the wordplay.
'off' becomes 'out' (both can mean wrong or inaccurate).
'cook' becomes 'do' (do can mean to cook).
'out'+'do'='OUTDO'
(Other definitions for outdo that I've seen before include "Surpass, go one better than" , "going to top?" , "Surpass someone at something" , "Br superior to (someone)" , "Be better in performance (than another person)" .)