Prepare a coup good-heartedly? (4,2)

I believe the answer is:

cook up

I'm a little stuck... Click here to teach me more about this clue!

'prepare' is the definition.
(cooking up is a kind of preparing)

'a coup good-heartedly?' is the wordplay.
I cannot quite see how this works, but
'good' could be 'ok' and 'ok' is found within the answer.
'a coup' could be 'coup' and 'coup' is found within the leftover letters.
No letters remain.
This explanation may well be incorrect...

Can you help me to learn more?

(Another definition for cook up that I've seen is " Devise".)

I've seen this clue in the Evening Standard.

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