Crossword Genius

Biscuit that's new behind unopened sponge cakes, filling hole (6,4)

Ross

I believe the answer is:

ginger snap

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'biscuit' is the definition.
(I've seen this before)

I don't understand how the remainder of the clue works.

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(Other definitions for ginger snap that I've seen before include "quick bite" , "Spicy biscuit" .)

I've seen this clue in The Guardian.
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