Cakes once cooked aboard ship (6)
I believe the answer is:
scones
'cakes' is the definition.
(type of small cake)
'once cooked aboard ship' is the wordplay.
'cooked' indicates an anagram (letters cooked into a new form).
'aboard' means one lot of letters goes inside another.
'ship' becomes 'SS' (prefix in ship names eg SS Great Britain).
'once' is an anagram of 'cone'.
'cone' placed inside 'ss' is 'SCONES'.
(Other definitions for scones that I've seen before include "Small soft cakes of flour, fat and milk - eaten buttered" , "Small flattish plain cake" , "Cakes for tea" , "Small unsweetened or lightly sweetened cakes" , "Small cakes of flour and fat, usually buttered" .)