Copper darts off - that covers dessert (7)
I believe the answer is:
custard
'dessert' is the definition.
(custard is a type of dessert)
'copper darts off that covers' is the wordplay.
'copper' becomes 'cu' (Cu is the chemical symbol for copper).
'off' is an anagram indicator.
'that covers' means one lot of letters goes inside another.
'darts' is an anagram of 'stard'.
'cu' inserted inside 'stard' is 'CUSTARD'.
(Other definitions for custard that I've seen before include "Pudding sauce" , "Pudding accompaniment" , "Sweet sauce made with milk and eggs" , "Egg/milk bake" , "Type of apple" .)