Mince pie, cold, is impressive (4)
I believe the answer is:
epic
'impressive' is the definition.
(I've seen this before)
'mince pie cold' is the wordplay.
'mince' indicates an anagram.
'cold' becomes 'c' (eg on taps).
'pie' anagrammed gives 'epi'.
'epi'+'c'='EPIC'
'is' is the link.
(Other definitions for epic that I've seen before include "imposing" , "Large-scale" , "Long poem set in nice picture" , "Long classic film" , "Heroic, huge" .)