Place cereal into an extra large mixing bowl and set aside.
Pour the powdered sugar into a 2-gallon re-sealable food storage plastic bag and set aside.
Place white chocolate chips and heavy cream together in a microwave-safe bowl; microwave on high for 45 seconds; stir. Continue to microwave in 15 second intervals until the chocolate has melted and the mixture can be stirred smooth.
Pour half the melted chocolate over the top of the cereal, gently fold with a spatula. Poor the remaining mixture over the top and gently fold to combine (doing this in two steps helps make sure all the cereal is evenly coated.)
Transfer the coated cereal to the bag with the powdered sugar; seal bag and gently toss until all the cereal is well-coated.
Place cereal back in the large bowl and toss with the pretzels, cranberries, and pistachios.