In a large microwave-safe bowl, microwave the peanut butter, white chocolate, and unsalted butter in 30-second intervals until melted, mixing in-between intervals until smooth.
Whisk in the vanilla extract.
Stir in the Chex cereal and toss to cover and coat the cereal.
Place coated cereal in a large ziplock bag. Add the powdered sugar, seal, and gently shake the bag around to coat the ingredients in the bag with the powdered sugar.
Place the coated cereal mix into a separate large bowl and allow the mix to cool for 5-10 minutes.
Add the M & M candies, chocolate-covered pretzels, and sprinkles. Gently toss together to mix the candies into the puppy chow. Serve.
Notes
Makes approximately 10-12 servingsStore in an airtight container at room temperature for up to one week.