Perhaps Robbie cut cakes as prepared in opulent mansion (3-1-4)

'prepared in opulent mansion' is the definition.
I don't know anything about this answer so I cannot tell whether it can be defined by this definition.

'perhaps robbie cut cakes as' is the wordplay.
I cannot quite understand how this works, but
'as' could be 'ala' (French 'a la' - 'in the style of') and 'ala' is present in the answer.
The remaining letters 'margo' is a valid word which might be clued in a way I don't understand.
This may be the basis of the clue (or it may be nonsense).

Can you help me to learn more?