Something frozen, cheese melting in it (3,5)
I believe the answer is:
ice sheet
'something frozen' is the definition.
I can't tell whether this definition defines the answer.
'cheese melting in it' is the wordplay.
'melting' is an anagram indicator.
'in' is an insertion indicator.
'cheese' is an anagram of 'ceshee'.
'ceshee' put within 'it' is 'ICE-SHEET'.
Can you help me to learn more?
(Other definitions for ice sheet that I've seen before include "Extensive frozen layer over land" , "Extensive frozen area" , "white surface layer" .)