Two sons leaving corks for hat (6)
I believe the answer is:
topper
'hat' is the definition.
(topper is a kind of hat)
I don't understand the rest of the clue.
(Other definitions for topper that I've seen before include "Type of hat (informal)" , "Hat for formal occasions" , "expensive hat" , "Informally a top hat or jolly good fellow" , "Informally a tall hat - the best" .)