1 cup unsalted butter, softened
1 cup firmly packed light brown sugar
1 1/4 teaspoons kosher salt
2 1/2 cups all-purpose flour
11 ounces butterscotch chips
3/4 cup light corn syrup
1 tablespoon plus 1 teaspoon water
2 cups roasted salted whole cashews
Preheat oven to 350°. Lightly grease a 9" x 13" pan with cooking spray. Line the pan with two sheets of parchment paper, creating a parchment sling. Spray parchment paper with cooking spray.
Cream butter, brown sugar, and salt using an electric mixer on medium speed for 1 to 1 & 1/2 minutes. Decrease mixer speed to low and add the flour. Mix just until combined.
Lightly press dough evenly into the prepared pan. Poke holes in the dough with a fork. Bake for 30 to 40 minutes, until the crust is a golden color. Remove to wire rack to cool.
Meanwhile, prepare the butterscotch topping combining butterscotch chips, corn syrup, and water in a heavy saucepan over low heat. Stir until mixture comes to a simmer and butterscotch chips are melted. Pour over crust.
Sprinkle cashews over the butterscotch caramel. Bake for 5 minutes. Cool completely on a wire rack. After cooling, remove from pan and use a very sharp knife to cut into bars.