Does stupendously well to steal small bust (6)

'does' is the definition.
Although both the answer and definition are verbs in their -s form, I cannot understand how they can define each other.

'stupendously well to steal small bust' is the wordplay.
I cannot quite understand how this works, but
'well' could be 'so' (I've seen this in other clues) and 'so' is located in the answer.
'small' could be 's' (abbreviation - e.g. clothes size) and 's' is present in the answer.
This may be the basis of clue (or it may be nonsense).

Can you help me to learn more?