Spray a 13x9-inch baking pan with nonstick spray and line with parchment paper. Set aside.
In a large pot or Dutch oven, combine the sugar and corn syrup. Bring to a full boil over medium-high heat, stirring constantly.
As soon as the mixture comes to a boil, remove from the heat and add the peanut butter, stirring until smooth and well combined.
Gradually fold in the Rice Krispies until well coated. Carefully pour into the prepared pan and press down with a greased spatula.
Let cool completely (about 1 hour) before cutting and serving.
Notes
Store in an airtight container for up to 1 week.The amount of Rice Krispies you use will determine how dry and dense the bars are. This recipe can take up to 18 ounces of Rice Krispies (a “family size” box) if you prefer lots of cereal in your bars, but note that the mixture will become very hard to stir.