Line a 15x10-inch baking pan with foil, extending the foil over the edges.
In a large saucepan, cook and stir granulated sugar and corn syrup over medium heat until the mixture begins to boil around the edges.
Cook and stir for an additional minute, then remove from heat.
Stir in peanut butter until the mixture is smooth.
Then, add the crisp rice cereal and cornflakes, mixing until they are evenly coated.
Transfer the mixture to the prepared pan and use a piece of waxed paper to press it firmly into the pan.