Basil and pine nut sauce (5)
I believe the answer is:
pesto
'basil and pine nut sauce' is the definition.
(I've seen this before)
This is all the clue.
(Other definitions for pesto that I've seen before include "Sauce of basil, pine nuts, etc" , "Saucy work" , "Sauce made of basil and cheese" , "Basil and pine nut sauce" , "A sauce served with pasta" .)