Productive hen (5)
I believe the answer is:
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">productive hen</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 layer that I've seen before include "Stratum; chicken" , "One of several thicknesses" , "Coating" , "Single thickness and hen" , "Tier or thickness - or a hen?" .)