Trattoria sauce (4)
(Other definitions for ragu that I've seen before include "pasta sauce" , "tomato and meat sauce" .)
'trattoria sauce' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for pesto that I've seen before include "sauce involving Basil" , "Pasta sauce variety" , "Sauce of basil, pine nuts, etc" , "Basic sauce" , "Sauce made of basil and cheese" .)