In a large microwave-safe bowl, heat the chocolate chips, peanut butter, and butter in 30-second increments in the microwave. Stir after each increment until smooth. Add the vanilla and stir to combine.
Add the Rice Chex cereal to the bowl and gently toss with a spatula to coat the cereal in the chocolate sauce.
When the cereal has been completely coated, spoon it into a large zip-lock bag. (You may have to do this in batches if the bag is not big enough to hold all the cereal). Pour in the confectioners' sugar and seal the bag.
Toss the cereal in the confectioners' sugar to coat.
When the cereal is completely coated in the confectioners' sugar, remove it from the bag and put it into a serving bowl.
Serve at room temperature. Makes 9 cups.
Substitute other types of Chex cereal (try Chocolate Chex if it's available!) or Crispix cereal, if desired.