French cake (6)
'french cake' is the definition.
(I've seen this in another clue)
This is the entire clue.
(Other definitions for gateau that I've seen before include "Rich dessert cake" , "Elaborate cake" , "named for Black Forest?" , "Richly decorated cake" , "Black Forest dessert" .)
(Another definition for galette that I've seen is " Savoury cake/pancake".)