Line 15x10x1-inch pan with foil, with ends of foil extending over sides; spray with cooking spray. Beat butter and sugar in large bowl with mixer until light and fluffy.
Add flour and salt; beat on low speed until well blended. Press onto bottom of prepared pan.
Bake 15 min. or until edges of crust are golden brown; sprinkle with chocolate. Cover.
Let stand 5 min. or until chocolate is melted; spread to evenly cover crust with chocolate. Refrigerate 15 min. or until chocolate layer is firm.
Microwave caramels and cream in microwaveable bowl on HIGH 2 min. or until caramels begin to melt; stir until caramels are completely melted and mixture is well blended. Gently spread caramel sauce over chocolate layer.
Sprinkle with nuts; press nuts into caramel layer with back of spoon to secure. Cool completely. Use ends of foil to remove dessert from pan before cutting into bars.
