Edible hat? (4-3)

I believe the answer is:

pork-pie

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This clue might be a double definition.

'edible' is the first definition.
The answer and definition can be both things that one consumes for nourishment as well as being singular nouns.
Perhaps you can see an association between them that I don't see?

'hat?' is the second definition.
Although both the answer and definition are singular nouns, I cannot see how one could define the other.

Can you help me to learn more?

I've seen this clue in the Evening Standard.

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