Foamy, but it can be hot if you cook the casing (6)

I believe the answer is:

frothy

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'foamy' is the definition.
(synonyms)

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

(Other definitions for frothy that I've seen before include "Leopard-like feline" , "Covered with foam, like superficial talk" , "Very bubbly" , "Sudsy" , "Foamy; insubstantial" .)

I've seen this clue in the Evening Standard.

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