Baby's biscuit (4)
I believe the answer is:
rusk
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">baby's biscuit</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 rusk that I've seen before include "Capital of Malta" , "Bread baked again until it is brown and hard" , "Hard bread given to babies" , "in Bristol Channel" , "Baby's dry biscuit" .)