Tasty treat turns out to be a cool cheat (9)
I believe the answer is:
chocolate
'tasty treat turns out to be a cool cheat' is the definition.
(I've seen this before)
This is all the clue.
(Other definitions for chocolate that I've seen before include "Sweet made with cacao beans" , "The tasty treat could turn out to be a cool cheat" , "Delicious food of roasted ground cacao beans" , "Coca hotel is a treat" , "Drink (if hot)" .)