Golden Gate – first, cake! (6)
I believe the answer is:
gateau
'cake' is the definition.
(I know that gateau is a type of cake)
'golden gate first' is the wordplay.
'golden' becomes 'au' (Au is the chemical symbol for gold).
'first' is a charade indicator (letters next to each other).
'au' after 'gate' is 'GATEAU'.
(Other definitions for gateau that I've seen before include "It's sweet" , "Black Forest dessert" , "Cake (from the Black Forest?)" , "Afternoon snack" , "Rich cream cake" .)