Breakfast for a while behind bars (8)

I believe the answer is:

porridge

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'breakfast' is the definition.
(porridge might be eaten for breakfast)

I cannot understand how the rest of the clue works.

Can you help me to learn more?

(Other definitions for porridge that I've seen before include "Breakfast dish - spell in prison" , "Cooked meal (served in prison?)" , "hot stuff?" , "Breakfast food - prison term" , "Hot breakfast food" .)

I've seen this clue in The Daily Express.

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