In another large bowl that is microwave-safe, combine chocolate chips, peanut butter and butter.
Microwave chocolate, peanut butter, and butter for 1 minute. Remove from microwave and stir, then microwave for 30 more seconds and stir again until the peanut butter mixture is completely smooth (it might only take the first minute of microwaving, every microwave is different).
Stir in vanilla extract with the chocolate. Pour melted chocolate slowly over Chex Mix cereal in the bowl, stirring carefully to coat cereal pieces evenly with chocolate.
Pour coated cereal mixture into large gallon Ziplock bag.
Add powdered sugar into the bag and seal bag closed. Now is the fun part - shake the bag all around to coat all of the cereal well.
Add Christmas m&m's and Reese's peanut butter cups to the Christmas snack mix and you are good to go!
Store leftovers in a ziploc bag or other airtight container. The Chex mix will last for up to 1 week. Enjoy one of our favorite holiday treats!
Notes
You can customize this recipe by adding your favorite mix-ins. We recommend the following: salty pretzels (pretzel sticks or mini pretzels work great), white chocolate chips, dash of holiday-colored sprinkles, mini marshmallows, nuts, or Cheerios cereal.