Ruin zest, an ingredient for cake? (8)

I believe the answer is:

marzipan

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'ingredient for cake?' is the definition.
I can't judge whether this definition defines the answer.

'ruin zest an' is the wordplay.
'ruin' becomes 'mar' (I've seen this before).
'zest' becomes 'zip' (I've seen this in another clue).
'mar'+'zip'+'an'='MARZIPAN'

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(Other definitions for marzipan that I've seen before include "that's sweet" , "Cake topping" , "Cake icing made of ground almonds and sugar" , "Ground almond paste" , "sort of sweet" .)

I've seen this clue in The Times.

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