Cooked eels with Coney Islander once (9)

I believe the answer is:

ceylonese

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'islander once' is the definition.
I can't judge whether this definition defines the answer.

'cooked eels with coney' is the wordplay.
'cooked' is an anagram indicator (letters cooked into a new form).
'with' says to put letters next to each other.
'eels' after 'coney' is 'coneyeels'.
'coneyeels' is an anagram of 'CEYLONESE'.

Can you help me to learn more?

(Another definition for ceylonese that I've seen is " Old islander".)

I've seen this clue in The Times and The Sunday Times.

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