In a small saucepan, melt the butter, honey, brown sugar and vanilla sugar over a medium heat. When it starts bubbling, reduce the heat and cook for three more minutes.
In the meantime, mix the oats and rice cereal in a large bowl.
Pour the contents of the saucepan over the dry ingredients, and mix well to ensure the oats and cereal are coated in the sticky mixture. Add the cranberries and stir. Leave to cool slightly for 5 minutes and add the white chocolate chips.
Pour into a 22 x 17cm (8.5x6.5 inches) rectangular dish and press down so it all sticks together (thickness of about 2cm, or ¾ in).
Cover and leave to cool at room temperature for two hours before cutting into bars. Store them at room temperature in an airtight container.
If your cereal bars are coming apart as you are cutting them, try pressing them down a bit more, and leaving them in the fridge for 20 minutes (do not leave them in there any longer or they will be rock hard!).