Step 1: Pour the Chex cereal into a very large mixing bowl. Ensure the bowl is large enough to allow for thorough mixing later.
Step 2: In a microwave-safe bowl, combine the chocolate chips, creamy peanut butter, and unsalted butter. Microwave on high for 60 seconds. Stir well until smooth. If not fully melted, microwave in additional 15-second intervals, stirring after each, until the mixture is completely smooth and glossy.
Step 3: Stir the vanilla extract into the melted chocolate-peanut butter mixture until fully combined.
Step 4: Pour the warm chocolate-peanut butter mixture over the cereal in the large bowl. Gently fold and stir with a rubber spatula until all the cereal pieces are evenly coated. Take your time to ensure full coverage.
Step 5: Divide the coated cereal into two large gallon-sized zip-top bags. Add 1/2 cup of confectioners’ sugar to each bag. Seal the bags, leaving some air, and shake vigorously until all the cereal is thoroughly coated with the sugar.
Step 6: Spread the Puppy Chow in a single layer on a large parchment-lined baking sheet. Allow it to cool completely at room temperature for 30-60 minutes, or refrigerate for 15-20 minutes, until the chocolate has set.
Step 7: Once cooled, break up any large clumps and transfer the Puppy Chow to an airtight container. Store at room temperature for up to one week or in the refrigerator for longer.