Line a large baking sheet with parchment paper and set it aside. This will be where the coated cereal mix dries and sets, so having it ready beforehand makes the process smoother.

In a large, microwave-safe bowl, combine the blue candy melts, peanut butter, and butter. Microwave in 30-second intervals, stirring well after each round, until everything is melted and smooth. This should take about 1 to 1½ minutes total. Be careful not to overheat, as candy melts can scorch easily. Once melted, stir in the vanilla extract for added flavor.

Pour the Rice Chex cereal into the bowl with the melted mixture. Gently toss with a spatula or large spoon until every piece is evenly coated. Work carefully to avoid breaking the cereal.

Divide the coated cereal into two batches for easier mixing. Transfer half of the cereal into a gallon-sized Ziploc bag. Add half of the powdered sugar, seal the bag tightly, and shake vigorously until the cereal is fully coated and no longer sticky.

Pour the coated cereal mixture onto the baking sheet. Repeat step 4 with the remaining half of the cereal and powdered sugar.

Transfer everything back into a large bowl. Gently fold in the broken Oreo and Chips Ahoy cookie pieces, making sure they are evenly distributed throughout the mix.

Spread the coated cereal mixture out evenly on the prepared baking sheet. Let it sit at room temperature for about an hour to allow the chocolate to set completely. If serving right away, sprinkle the candy eyeballs over the mix for that signature Cookie Monster look. If you’re storing it for later, wait to add the candy eyeballs until just before serving - otherwise, they might get buried beneath the mix.

Keep the Cookie Monster Puppy Chow in an airtight container at room temperature for up to a week. Serve in a large bowl for sharing, or portion it into small bags for a fun and easy grab-and-go snack.