Remains of cake grew mouldy (8)
I believe the answer is:
wreckage
'remains' is the definition.
(I've seen this before)
'cake grew mouldy' is the wordplay.
'mouldy' indicates anagramming the letters.
'cake'+'grew'='cakegrew'
'cakegrew' anagrammed gives 'WRECKAGE'.
'of' is the link.
(Other definitions for wreckage that I've seen before include "Ruin" , "Broken bits and pieces" , "Sign of misfortune at sea" , "Ruined material" , "Ruined remains" .)