Scotcheroos

Cooking spray for greasing pan

1 1/4 cup light corn syrup (11 1/2 ounces; 324 g), such as Karo 

7 1/2 ounces brown sugar (215 g; about 3/4 cup loosely packed)

9 ounces (255 g; 1 cup) creamy peanut butter (commercial or natural varieties will both work well)

2 teaspoons (10 ml) vanilla extract

1 teaspoon (4 g) Diamond Crystal kosher salt; for table salt, use about half as much by volume or the same weight

6 cups (180 g) rice crisp cereal such as Rice Krispies

8 ounces (225 g) butterscotch chips

8 ounces (225 g) bittersweet chocolate, 60% cacao, roughly chopped 

Flaky sea salt, such as Maldon, to finish, optional

Lightly grease a 9-by-13-inch baking pan with cooking spray; set aside. In a minimum 3-quart saucepan or Dutch oven, heat corn syrup and sugar over medium heat, whisking occasionally, until mixture is just bubbling around the edges, about 2 minutes.

Slowly whisk in peanut butter, vanilla, and kosher salt until peanut butter is completely incorporated and mixture is smooth, about 30 more seconds.

Off heat, fold in rice cereal with a rubber spatula. Transfer mixture to the greased pan and pat gently into place (do not overpack).

In a heatproof bowl, melt chocolate and butterscotch chips in microwave in 15-30 second intervals, stirring thoroughly between each interval, until glossy and smooth. Pour over cereal and use rubber spatula to spread topping across the bars in a thin, even layer. Sprinkle flaky salt over topping, if desired.

Let scotcheroos rest at room temperature for at least 2 hours or until topping is firm and set. Cut into roughly 2-inch squares and serve.