Large hard sweet (10)
I believe the answer is:
gobstopper
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">large hard sweet</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 gobstopper that I've seen before include "Large, hard sweet to suck" , "Large, hard spherical sweet" , "Hard round sweet" , "Big sweet" .)