Decorate a cake (3)
I believe the answer is:
ice
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">decorate a cake</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 ice that I've seen before include "Finish decorating the Christmas cake" , "Top cake" , "Diamonds (sl)" , "Diamonds (informal)" , "Formality" .)