Simper stupidly as one prepares (6)

I believe the answer is:

primes

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'prepares' is the definition.
(priming is a kind of preparing)

'simper stupidly' is the wordplay.
'stupidly' indicates an anagram.
'simper' with letters rearranged gives 'PRIMES'.

'as one' is the link.
I am not very happy about this link. Some or all of it may be part of another bit of the clue.

Can you help me to learn more?

(Other definitions for primes that I've seen before include "Prepares something for action - perhaps a pump" , "best parts" .)

I've seen this clue in the Evening Standard.

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