Prepare the pan: Grease a 9×½13-inch baking pan with butter or cooking spray. Set aside.

Melt peanut butter mixture: In a large saucepan, combine sugar and corn syrup over medium heat. Stir constantly until the sugar dissolves and the mixture begins to bubble (about 3–4 minutes). Remove from heat and stir in peanut butter until smooth and fully incorporated.

Coat the cereal: Place crispy rice cereal in a large mixing bowl. Pour the warm peanut butter mixture over the cereal. Using a spatula or wooden spoon, gently fold and stir until the cereal is evenly coated. Work quickly before the mixture cools and hardens.

Press into pan: Transfer the mixture to the prepared baking pan. Press firmly and evenly into the pan using the back of a spoon or your hands (lightly greased).

Melt chocolate topping: In a microwave-safe bowl or saucepan, combine chocolate chips and butterscotch chips (if using). Melt in the microwave in 30-second intervals, stirring between each, until smooth. Alternatively, melt over low heat on the stovetop, stirring constantly.

Top and chill: Pour the melted chocolate over the pressed cereal base. Use a spatula to spread the chocolate evenly to the edges. Refrigerate the pan for 30–60 minutes, or until the chocolate is set.

Cut and serve: Using a sharp knife (dipped in hot water and wiped dry between cuts), cut into 24 squares. Serve immediately or store in an airtight container.