Italian basil sauce (5)
I believe the answer is:
pesto
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">italian basil sauce</span>' is the definition.<br/ ><span class="explanation-format__explanation">(I've seen this before)</span><br/ ><br/ >This is all the clue.<br/ ></span>
(Other definitions for pesto that I've seen before include "Pasta sauce mainly of basil and cheese" , "Basil-based sauce" , "Sauce made of basil and cheese" , "Basic sauce" , "Italian sauce containing basil" .)