In medium bowl, mix flour, brown sugar and salt. Cut in the 1/2 cup butter until evenly mixed. Press evenly in bottom of an ungreased 13" x 9" baking pan. Bake at 350 for 15 minutes; allow to cool slightly.
Sprinkle nuts evenly over semi-cooled crust.
In 1-quart saucepan, heat all remaining ingredients over low heat, stirring occasionally, just until chips are melted. Drizzle the melted butterscotch mixture evenly over nuts. Bake at 350 for about 5 minutes.
For best results, cut into bars while they are still warm.