Food lassie thus prepared without stale ingredients (5)

I believe the answer is:

sushi

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'food' is the definition.
(sushi is a kind of food)

I cannot understand how the rest of the clue works.

(Other definitions for sushi that I've seen before include "put away in Japan" , "Exotic food" , "cold food" , "fare from Japan" , "Japanese cuisine" .)

I've seen this clue in The Daily Express.

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