Sweet I stuff into ill-fitting suit (8)
I believe the answer is:
tiramisu
'sweet' is the definition.
(type of dessert or sweet)
'i stuff into ill-fitting suit' is the wordplay.
'stuff' becomes 'ram' (ramming is a kind of stuffing).
'into' is an insertion indicator.
'ill-fitting' is an anagram indicator.
'i'+'ram'='iram'
'suit' anagrammed gives 'tisu'.
'iram' put within 'tisu' is 'TIRAMISU'.
(Other definitions for tiramisu that I've seen before include "Italian sponge pudding" , "Rich dessert, it is a rum (anag.)" , "Rich Italian dessert" , "Italian dessert of cake, coffee and chocolate" , "Italian dessert with coffee and liqueur" .)