Step 1: Measure 9 cups of crispy rice cereal into a very large bowl and set aside.
Step 2: In a medium microwave-safe bowl, combine the chocolate chips, creamy peanut butter, and butter. Microwave on high for 30 seconds. Stir well. Continue microwaving in 15-second intervals, stirring after each, until the mixture is smooth and completely melted (usually 1-2 minutes total). Stir in the vanilla extract.
Step 3: Pour the melted chocolate-peanut butter mixture over the cereal in the large bowl. Using a large spoon or rubber spatula, gently fold and stir until the cereal is evenly coated.
Step 4: Divide the coated cereal evenly into two large (1-gallon) resealable plastic bags.
Step 5: Add 3/4 cup powdered sugar to each bag. Seal the bags, ensuring there's plenty of air inside, and shake vigorously until the cereal pieces are completely coated with powdered sugar.
Step 6: Spread the finished puppy chow onto a baking sheet lined with parchment paper or wax paper to cool completely, which helps the coating set and prevents sticking.
Step 7: Once cooled, transfer the puppy chow to an airtight container. Store at room temperature for up to one week.