Lightly grease a 9×13-inch baking pan with butter or nonstick spray, or line it with parchment paper for easy removal. Add the crispy rice cereal to a large mixing bowl and set aside.

In a medium saucepan, combine the granulated sugar and light corn syrup. Cook over medium heat, stirring often, until the mixture just starts to bubble around the edges and the sugar has fully dissolved. Do not let it come to a full rolling boil to keep the bars soft and chewy.

Remove the pan from the heat as soon as the mixture starts to bubble and looks clear. Immediately stir in the peanut butter and vanilla extract until the mixture is smooth and creamy.

Pour the warm peanut butter mixture over the cereal in the large bowl. Working quickly, use a sturdy spatula or wooden spoon to stir until all of the cereal is evenly coated.

Transfer the coated cereal mixture to the prepared 9×13-inch pan. Gently press it into an even layer using lightly buttered fingertips or a piece of parchment paper. Do not press too firmly to avoid making the bars too hard.

In a microwave-safe bowl, combine the semi-sweet chocolate chips and butterscotch chips. Microwave on 50% power in 30-second intervals, stirring after each, until melted and smooth (about 60–90 seconds total). Alternatively, melt in a heat-safe bowl set over a pan of barely simmering water, stirring until smooth.

Pour the melted chocolate–butterscotch mixture over the cereal layer. Use an offset spatula or the back of a spoon to spread it into an even layer all the way to the corners. If desired, sprinkle a small pinch of flaky sea salt over the top. Let the bars cool at room temperature for 1–2 hours, or until the topping is set and firm. You can speed this up by chilling in the refrigerator for 20–30 minutes.

Once the topping is fully set, use a sharp knife to cut the Scotcharoos into squares or rectangles. For cleaner slices, warm the knife under hot water, dry it, and press straight down. Serve and enjoy.