Layer cake less filling, therefore (5)
I believe the answer is:
hence
'therefore' is the definition.
(I know that therefore can be written as hence)
'layer cake less filling' is the wordplay.
'layer' becomes 'hen' (something which lays - eggs in this case).
'less filling' suggests removing the centre (letters which fill the word are removed).
'cake' with its centre taken out is 'ce'.
'hen'+'ce'='HENCE'
(Other definitions for hence that I've seen before include "It follows from that fact" , "Therefore, consequently" , "For this reason; in the future" , "As a consequence" , "Thus" .)