Doubt about ''of which''

[GuilhermeRM]

Hello, I couldn't understand the rule about using ''of which'': '' The phrase of which is nonstandard usage when referring to a singular noun''. May someone clarify it to me? Thank you.

[Rover_KE]

Where did you encounter that 'rule'? It's nonsense.

'She brought a cake which I took a big slice of'

equates to

'She brought a cake, of which I took a big slice'.

Rover