Hi Maddy,
you could try converting the Melt & Mix Chocolate Chunk Mud Cake I posted on this forum to a white chocolate version. Don't know why I haven't given it a go but would be interested to hear your results if you decide to give it a try. The original recipe is made with dark chocolate but I always use a mix of milk chocolate and either peppermint or caramel but I think you could just add extra flour in place of the cocoa and maybe increase the amount of actual chocolate. Interested to know what you think. I do have a friend who has a white chocolate mud cake recipe so I'll also email her and see if she is willing to share it. She has just got a TMX so would probably be happy for someone to do a conversion of it for her.
Cheers,
Roxy