In a large pot set over medium heat, combine the granulated sugar and light corn syrup. Continuously stir the mixture until it reaches a rolling boil, ensuring it doesn't stick to the bottom of the pot.
Once the mixture is boiling, promptly remove the pot from the heat and stir in the peanut butter. Mix vigorously until the peanut butter is fully melted and the mixture is smooth and homogeneous.
Gently fold in the Rice Krispies cereal, ensuring all the cereal is coated with the peanut butter mixture. Be careful not to crush the cereal as you mix.
Prepare a 9x13 inch baking dish by lining it with parchment paper, allowing extra paper to hang over the edges for easy lifting later. Transfer the cereal mixture into the dish, pressing it down firmly and evenly using the back of a spatula or your clean hands for an even surface.
In a microwave-safe bowl, combine the semisweet chocolate chips, butterscotch chips, and a pinch of flaky sea salt. Microwave in 30-second intervals, stirring between each, until the chips are completely melted and the mixture is smooth and glossy.
Drizzle the melted chocolate-butterscotch mixture over the pressed cereal layer. Use a spatula to spread it out evenly, covering the top of the Scotcheroos.
Allow the Scotcheroos to cool at room temperature for about 1 hour, or until the topping is set and firm to the touch.
Once fully set, use the parchment paper to gently lift the Scotcheroos out of the baking dish. Cut into squares or bars, adjusting the size to your preference.
Notes
For an indulgent touch, drizzle additional melted chocolate and butterscotch over the top just before serving.