Hams cooked with potatoes (4)
I believe the answer is:
mash
'potatoes' is the definition.
(mashed potato)
'hams cooked' is the wordplay.
'cooked' indicates an anagram (letters cooked into a new form).
'hams' anagrammed gives 'MASH'.
'with' acts as a link.
(Other definitions for mash that I've seen before include "Soft, pulpy mass" , "Crush, potatoes say" , "Food for horses" , "Pureed potato" , "TV series" .)