How to finish off a cake (3)

I believe the answer is:

ice

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'finish off a cake' is the definition.
(I've seen this in another clue)

I can't explain the remainder of the clue.

(Other definitions for ice that I've seen before include "Solid water" , "A state of water" , "To put in a drink or slide on" , "Chill - harden" , "Decorate with frosting" .)

I've seen this clue in The Globe and Mail.

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