Cutting down what the pastrycook may need (10)

I believe the answer is:

shortening

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'cutting down' is the definition.
(shortening is a kind of cutting down)

I cannot understand how the rest of the clue works.

(Other definitions for shortening that I've seen before include "reducing" , "fat used in pastry" , "Cutting out" .)

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

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