Schmear topper (3)
I believe the answer is:
lox
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">schmear topper</span>' is the definition.<br/ ><span class="explanation-format__explanation">(I've seen this in another clue)</span><br/ ><br/ >This is all the clue.<br/ ></span>
(Other definitions for lox that I've seen before include "Taxi's passenger" , "Smoked salmon" , "Rocket fuel" , "may come from the deli" .)