Crossword Genius

Rarely dancing on ice with an Elvis number? (4,2,1,4,4)

Ross

I believe the answer is:

once in a blue moon

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

'rarely' is the definition.
(I've seen this in another clue)

'dancing on ice with an elvis number?' is the wordplay.
I cannot really understand how this works, but
'on' is within the answer.
an anagram of 'ice' is 'cei' which is within the answer.
'an' could be 'a' and 'a' is present in the answer.
'number?' could be 'm' (M is an example) and 'm' is found in the answer.
This may be the basis of the clue (or it may be nonsense).

Can you help me to learn more?

(Other definitions for once in a blue moon that I've seen before include "with extremely low frequency'" , "on very rare occasions" , "Hardly ever (4,2,1,4,4)" , "very occasionally" , "very rarely" .)

I've seen this clue in The Independent.
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