1Heat oven to 350°F (325°F for dark or nonstick pan). Spray bottom and sides 13x9-inch pan with cooking spray. Make brownie batter as directed on box. Spread 1/2 of batter in pan. Bake 12 minutes.
2Meanwhile, in medium microwavable bowl, microwave caramels and whipping cream uncovered on High 2 to 3 minutes, stirring occasionally, until smooth.
3Pour caramel over partially baked brownie; spread to within 1/4 inch of edges. Sprinkle with 1 cup of the chocolate chunks and 1/2 cup of the pecans. Drop remaining brownie batter by small spoonfuls onto caramel layer. Sprinkle with remaining 3/4 cup chocolate chunks and 1/2 cup pecans.
4Bake 32 to 35 minutes longer or until center is almost set. Cool 1 hour at room temperature. Cover; refrigerate 1 hour before serving. For brownies, cut into 6 rows by 4 rows. Store covered at room temperature.