A layer of rich enamel (3)
I believe the answer is:
hen
'a layer' is the definition.
(something which lays - eggs in this case)
'of rich enamel' is the wordplay.
'of' says the answer is hidden in the clue.
'HEN' is hidden in the letters of 'rich enamel'.
(Other definitions for hen that I've seen before include "Clucking female" , "Domestic fowl" , "Source of eggs" , "Farm bird" , "Adult female chicken" .)