In a microwave safe dish, melt the white chocolate with 1 tbsp of butter and ¼ cup peanut butter. Melt in intervals of 20 seconds until smooth. Add ¼ tsp peppermint extract, stir, and set aside. After adding the extracts, the mixture may get "thick," but that's okay!
Next melt the semisweet chocolate chips in a microwave dish, along with the remaining 1 tbsp of butter and ¼ cup peanut butter. Melt in intervals of 20 seconds until smooth. Add ¼ tsp peppermint extract, stir, and set aside.
Add both the melted chocolate mixtures into a large bowl with the rice chex cereal. Stir with a spoon until the cereal is fully coated in the melted chocolates.
Finally add the M&M's and powdered sugar. Cover the bowl and shake until the powdered sugar is fully coating the puppy chow. If you do not have a big bowl with a cover, you can add the puppy chow to a gallon-sized plastic bag, seal, and shake to coat that way too.