Sweet spread for sandwiches, badly wrapped (8)
I believe the answer is:
pastille
'sweet' is the definition.
(pastille is a kind of sweet)
'spread for sandwiches badly wrapped' is the wordplay.
'spread for sandwiches' becomes 'paste'.
'badly' becomes 'ill' ('ill' can be adverbial as in 'ill-advised').
'wrapped' indicates putting letters inside.
'paste' going around 'ill' is 'PASTILLE'.
(Other definitions for pastille that I've seen before include "tablet" , "Small, often medicated, sweet" , "Small sweet/lozenge" , "One medicated sweet is the alternative" , "Cough lozenge" .)