Line 13×9-inch pan with foil, with ends of foil extending over sides. Grease foil. Microwave chocolate and butter in large microwaveable bowl on HIGH 2 min. or until butter is melted. Stir until chocolate is completely melted. Add sugar and eggs; mix well. Stir in flour until well blended. Spread half the batter into prepared pan.
Bake 25 min. or until top is firm to the touch. Meanwhile, microwave caramels and cream in medium microwaveable bowl on HIGH 2 min. or until caramels begin to melt; stir until caramels are completely melted. Stir in 1 cup nuts.
Spread caramel mixture over brownie layer in pan; cover with remaining brownie batter. (Some caramel mixture may peek through.) Sprinkle with remaining nuts. Bake 30 min. or until top is firm to the touch. Cool in pan on wire rack. Lift brownies from pan with foil handles before cutting into squares.