Welcome to the Cake Decorators Q&A
White Chocolate Ganache filling
How long can a cake with White Chocolate Ganache filling last?
Will the ganache filling harden like chocolate bar after couple of hours?
Can Paul's recipe of 900g of white chocolate to 400g of double cream be used as filling the centre of the caKE and also for Ganaching the sides of the cake?
The ganache will be fine for as long as the expiry date of the cream. The sugars in the white chocolate act as a preservative and keep the ganache fairly stable at room temperature. You'll soon know if it has gone off because it will smell or start sprouting fungus! You can use Paul's ganache ratios for both internal and external decorating. White chocolate won't go hard inside the cake, it will be a fudgy consistency.
There's a ganache quantities chart for different size cakes and blog here:
To learn a little about ganache shelf life have a peek here:
Hope this helps.