Butter 9x13-in pan. Set aside. In large bowl, combine flour, brown sugar, butter and salt. Using pastry blender or fork, cut in butter until mixture resembles coarse crumbs. Pat into bottom of prepared pan. Bake crust for 10 minutes or until golden brown. Remove from oven. (leave oven on).
To make topping:
Meanwhile, combine chips, corn syrup and butter in saucepan. Melt ingredients over medium heat. Remove from heat. Add vanilla.
Remove crust from oven. Sprinkle with nuts. Pour topping over nuts. Bake 10 minutes. Cut into squares while still warm.
Use 6 oz. butterscotch for lighter flavor; use 12 oz for a richer taste.