PM devouring every island's dessert (5,5)
I believe the answer is:
peach melba
'dessert' is the definition.
'pm devouring every island's' is the wordplay.
'devouring' means one lot of letters goes inside another.
'every' becomes 'each' (synonyms).
'island' becomes 'elba' (I've seen this before).
'pm' going around 'each' is 'peachm'.
'peachm'+'elba'='PEACH MELBA'
(Other definitions for peach melba that I've seen before include "Sweet" , "Dame Nellie's dish" , "Ice cream dish with fruit" , "fruity dessert" .)