Combine peanut butter, sugar, and corn syrup in a large microwave-safe bowl (can also heat over the stove on low-medium heat) for 60-90 seconds. Stir. It does not need to simmer or boil; it just needs to heat up enough for the mixture to be creamy and smooth.
Add cereal and stir.
Press the mixture into a greased 9x13" baking dish or a baking dish lined with parchment paper.
Melt chocolate chips and peanut butter chips in a double boiler or microwave. I usually use my microwave and heat the chocolate chips and peanut butter chips for 30 seconds, then I stir and heat them for an additional 15-20 seconds. Every microwave is different; my advice is to go low and slow—short intervals, stirring until smooth and creamy. DO NOT OVERHEAT CHOCOLATE.
Spread melted chocolate mixture over a pan of cereal bars. Allow the chocolate to set up completely before cutting the bars into 48 small squares. You can place the pan in the refrigerator to speed up the process.
Video
Notes
Store cereal bars in an airtight container for up to 3 days. Bars will start out crispy and soften slightly on the second day.