Preheat oven to 350°. Spray a 9″x 13″ pan with cooking spray. Using two sheets of parchment paper, line the pan’s width and length, creating a parchment “sling.” Spray parchment paper with cooking spray.
Using an electric mixer on medium speed, beat butter, brown sugar, and salt 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.
In a heavy saucepan over low heat, stir together butterscotch chips, corn syrup, and water. 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.
Makes 2 dozen 2-inch bars.