Some grapes topping sauce (5)
I believe the answer is:
pesto
'sauce' is the definition.
(I've seen this before)
'some grapes topping' is the wordplay.
'some' says the answer is hidden in the clue (some of the parts of the word are used).
'PESTO' is hidden in the letters of 'grapes topping'.
(Other definitions for pesto that I've seen before include "Basic sauce" , "A sauce served with pasta" , "Basil and pine nut sauce" , "Green sauce" , "Pasta sauce variety" .)