Dark treacle (8)
I believe the answer is:
molasses
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">dark treacle</span>' is the definition.<br/ ><span class="explanation-format__explanation">(I've seen this before)</span><br/ ><br/ >This is the entire clue.<br/ ></span>
(Other definitions for molasses that I've seen before include "Dark syrup from raw sugar" , "Slow runner" , "What's sweet" , "Black treacle" , "Thick treacle left over after refining raw sugar" .)