Prized subterranean fungus (7)
I believe the answer is:
truffle
'prized subterranean fungus' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for truffle that I've seen before include "Underground delicacy" , "Soft chocolate; fungus" , "Rich-flavoured fungus that grows undergrond" , "Fretful for tasty underground fungus" , "fungal growth" .)