PREHEAT oven to 350º F. Grease 9-inch springform pan.
MICROWAVE 1 cup chocolate pieces in small, uncovered, microwave-safe bowl on MEDIUM-HIGH (70%) power for 1 minute; STIR. Pieces may retain some of their original shape. If necessary, microwave at additional 10- to 15-second intervals, stirring just until smooth; cool to room temperature.
COMBINE flour, baking powder and salt. Beat brown sugar and butter in medium mixer bowl on high until creamy. Add eggs and beat until light and fluffy. Beat in melted chocolate. Add flour mixture and stir until blended. Stir in 1/2 cup pecans. Spread into prepared pan. Sprinkle with remaining 1/2 cup pecans and 1/3 cup chocolate pieces.
BAKE for 33 to 35 minutes or until wooden pick inserted in center comes out clean. Cool for 30 minutes; remove ring.
MICROWAVE remaining chocolate in small, heavy-duty plastic bag. Microwave on HIGH (100%) power for 30 seconds; knead. If necessary, microwave at additional 10- to 15-second intervals; kneading until smooth. Cut tiny corner from bag; squeeze to drizzle over brownie.
MICROWAVE caramels and milk in a small, uncovered, microwave-safe bowl on MEDIUM-HIGH (70%) power for 20 seconds; STIR. If necessary, microwave at additional 5- to 10-second intervals; stirring until smooth. Drizzle over brownie. Cut into slices.