Preheat oven to 350°. In a small bowl, combine flour, brown sugar and salt. Cut in 1/2 cup butter until mixture resembles coarse crumbs. Press into a greased 13x9-in. baking pan. Bake for 10 minutes., Meanwhile, in a microwave, melt butterscotch chips and remaining butter; stir until smooth. Stir in corn syrup. , Sprinkle nuts over crust; top with butterscotch mixture. Bake until set, about 10 minutes. Cool on a wire rack. Cut into bars.