Not half bad! (informal) (4-2)

I believe the answer is:

slap-up

(Other definitions for slap-up that I've seen before include "(Of meal) large/lavish" , "Lavish (colloq.)" , "Of meal, rich and plentiful" , "With no expense spared" , "Luxurious (feast)" .)

I've seen this clue in The Guardian.

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