In a microwave-safe bowl, combine 1 cup white chocolate chips, 1/2 cup creamy peanut butter, and 1 tablespoon vegetable oil. Microwave on high for 30 seconds, stir, then continue microwaving in 15-second intervals until the mixture is melted and smooth, about 60 seconds total.
While the chocolate mixture is melting, pour 9 cups Chex cereal into a large mixing bowl.
Pour the melted white chocolate mixture over the 9 cups Chex cereal and gently stir until all of the cereal is evenly coated.
Add 1 cup powdered sugar to one 1-gallon zip-top bag. Transfer half of the coated cereal to the bag, seal, and shake until well coated. Repeat with the remaining 1 cup powdered sugar, the remaining coated cereal, and the second 1-gallon zip-top bag.
Spread the coated cereal onto a parchment paper-lined baking sheet and let it cool completely.
Once the puppy chow has cooled, add 1 1/2 cups pastel M&M's and gently stir until evenly combined.
Store the puppy chow in an airtight container for up to 1 week.
Video
Notes
Store in air tight container for up to 1 week. If you kitchen is warmer, store in the refrigerator.