Hard brittle toffee (12)
I believe the answer is:
butterscotch
'hard brittle toffee' is the definition.
(I've seen this before)
This is all the clue.
(Other definitions for butterscotch that I've seen before include "confectionery" , "Brittle, yellow-brown sweet" , "Type of toffee" , "Kind of toffee" , "Hard brittle toffee" .)