Undercooked part of dish (7)
I believe the answer is:
rarebit
'dish' is the definition.
(rarebit is a kind of dish)
'undercooked part' is the wordplay.
'undercooked' becomes 'rare' (I've seen this before).
'part' becomes 'bit' (bit is a kind of part).
'rare'+'bit'='RAREBIT'
'of' is the link.
(Other definitions for rarebit that I've seen before include "Welsh food?" , "Cheese/toast savoury" , "which the Welsh take down?" , "Simple dish" , "cheesy meal" .)