Spray a 9×13 inch baking pan with vegetable spray. In a large mixing bowl, combine cake mix and brown sugar; blend. Add butter and eggs and beat with an electric mixer at medium speed for 3 to 4 minutes. Stir in nuts and mix completely. Spread batter evenly into pan (batter will be stiff). Bake at 350 degrees for 35 to 40 minutes or until bites test done. Cool completely in pan and cut into bite-sized pieces. Store in air-tight container.