Green sauce (5)
I believe the answer is:
pesto
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">green 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 "Sauce made of basil and cheese" , "sauce involving Basil" , "Pasta sauce variety" , "Sauce of basil, pine nuts, etc" , "Pasta sauce mainly of basil and cheese" .)