Heat oven to 350°F.
Line 13x9-inch pan with foil, with ends of foil extending over sides. Spray foil with cooking spray. Microwave chocolate and butter in large microwaveable bowl on HIGH 2 min. or until butter is melted. Stir until chocolate is completely melted and mixture is well blended. Add sugar and eggs; mix well. Stir in flour until blended. Pour 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 and mixture is well blended. 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. Use foil handles to remove brownies from pan before cutting to serve.