Sweet; fungus (7)
I believe the answer is:
truffle
This clue is a double definition.
'sweet' is the first definition.
(truffle is a kind of sweet)
'fungus' is the second definition.
(I know that truffle is a type of fungus)
(Other definitions for truffle that I've seen before include "Underground delicacy" , "Fungoid delicacy" , "Earthnut" , "Fungus, a delicacy" , "Valued culinary fungus" .)