Instructions: Center a rack in the oven; preheat the oven to 350 degrees. Butter a 13-by-18-inch jellyroll pan, including sides.

To prepare the crust: In a mixer with a paddle or in a bowl with a rubber spatula, beat 1 cup plus 2 tablespoons butter and brown sugar together until smooth. Stir salt into flour, then add flour to butter mixture. Mix until dough is well combined but still crumbly; if dough is mixed until a ball forms, crust will be tough.

Pat dough evenly along bottom of buttered pan, taking care not to pack dough down. Bake 5 minutes. With a fork, prick dough deeply all over. Return pan to oven; bake until dough is lightly browned, dry and no longer soft to the touch, about 7 minutes. Transfer to a cooling rack; do not turn off the oven.

To prepare butterscotch topping: In a large saucepan, combine remaining 3 1/2 tablespoons butter, butterscotch chips, corn syrup and 1 tablespoon plus 2 1/2 teaspoons water. Cook over medium heat, stirring constantly, until butter and butterscotch chips are melted, about 5 minutes. Pour topping over crust, using a spatula to spread evenly all the way to the corners. Sprinkle cashew pieces on top, pressing down lightly.

Bake until topping is bubbly and cashews are lightly browned, 11 to 13 minutes. Transfer to a rack; let cool completely before cutting into 2-by-3-inch bars.

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