Frozen dessert hardened around sphere (6)
I believe the answer is:
sorbet
'frozen dessert' is the definition.
(I know that sorbet is a type of frozen dessert)
'hardened around sphere' is the wordplay.
'hardened' becomes 'set' (synonyms).
'around' means one lot of letters goes inside another.
'sphere' becomes 'orb' (orb is a kind of sphere).
'set' placed around 'orb' is 'SORBET'.
(Other definitions for sorbet that I've seen before include "Granita-like dessert" , "Fruit water-ice" , "Sweet" , "Mushy ice drink to cleanse the palate" , "Strobe (anag.)" .)