Add the cereal, cranberries and white chocolate chips into a large bowl.
In a large micro-wave bowl, add the marshmallows and butter. Microwave on high for 3 minutes. Stir the mixture after two minutes. Stir in the vanilla at the end of the cooking time.
Pour the melted marshmallows into the large bowl containing the cereal mixture.
Stir with a wooden spoon to combine.
Transfer to a 9"x13" buttered rectangular pan and pat down evenly with your hands or a wooden spoon.