When the food is cooked, slipping off (3-5)

I believe the answer is:

non-stick

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'food is cooked slipping off' is the definition.
I know nothing about this answer so I can't tell whether it can be defined by this definition.

'when the' is the wordplay.
I cannot really understand how this works, but
'when' could be 'on' (I've seen this in other clues) and 'on' is present in the answer.
'the' could be 't' (the is pronounced as a 't' sound in some dialects) and 't' is found in the answer.
This explanation may well be incorrect...

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I've seen this clue in the Evening Standard.

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