Meal consumed by Asterix, say, failing to finish cake (6)
I believe the answer is:
gateau
'cake' is the definition.
(gateau is a kind of cake)
'meal consumed by asterix say failing to finish' is the wordplay.
'meal' becomes 'tea' (tea is a kind of meal).
'consumed by' indicates putting letters inside.
'asterix say' becomes 'Gaul' (Asterix is a Gaul in a series of comic books).
'failing to finish' means to remove the last letter.
'gaul' with its last letter taken away is 'gau'.
'tea' put within 'gau' is 'GATEAU'.
(Other definitions for gateau that I've seen before include "Cream dessert cake" , "It's sweet" , "Elaborate cake" , "Gooey cake" , "Fancy cake" .)