Proving to be, on unmoulding (7,3)

I believe the answer is:

turning out

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

'proving' is the definition.
('turn out' can be a synonym of 'prove')

'be on unmoulding' is the wordplay.
I cannot quite understand how this works, but
'be' could be 'go' (going is a kind of being) and 'go' is found within the answer.
This may be the basis of the clue (or it may be nonsense).

'to' is the link.

Can you help me to learn more?

I've seen this clue in the Evening Standard.

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