These no-bake cereal bars with peanut butter, butterscotch and chocolate are a Midwest classic! When my Aunt Annie makes a double (or triple!) batch of these for our family, we can barely let the chocolate set before we all dive in.
Line a 9-by-13-inch baking dish with parchment paper, leaving a 2-inch overhang on the two long sides. Spray with nonstick cooking spray.
Combine the corn syrup with the sugar in a large pot. Cook over medium heat, stirring occasionally, until the sugar is dissolved, 3 to 5 minutes. (It’s better to err on the side of lower heat here because if the mixture boils for too long, the bars will be incredibly hard to cut!)
Remove the pot from the heat and add the peanut butter. Stir until combined. Add the cereal and stir until coated. Pour into the prepared baking dish and spread evenly with a spatula.
Combine the chocolate and butterscotch chips in a medium microwave-safe bowl. Microwave in 30-second intervals, stirring each time, until totally melted (about 2 minutes total). Pour over the cereal mixture, spread evenly and let sit at room temperature until the chocolate-butterscotch topping has firmed, about 2 hours (or refrigerate until chilled, about 2 hours).
Use the parchment overhang to help lift the mixture out of the pan. Cut into 15 to 20 bars. Store in an airtight container at room temperature for up to 3 days. Or freeze for up to 1 month.