Biscuit offered by Spooner's royal Arab leader? (9)

I believe the answer is:

shortcake

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'biscuit' is the definition.
(I know that shortcake is a type of baking-powder biscuit)

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

Can you help me to learn more?

(Other definitions for shortcake that I've seen before include "Rate shock (anag)" , "it crumbles!" , "Sweet biscuit - rat chokes (anag)" , "pastry?" , "Dessert from America" .)

I've seen this clue in The Telegraph.

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