1. Combine flour, cocoa, baking powder and salt in medium bowl. Beat sugar, butter and vanilla in large mixer bowl. Add egg one at a time, beating well after each addition. Gradually beat in flour mixture. Stir in1 1/2 cups morsels. Pour into greased 9-inch-square baking pan.
2. Bake in preheated 350F oven for 25-30 minutes or until wooden pick inserted near center comes out slightly sticky. Cool in pan on wire rack (brownies will sink in center when cooled).
3. Microwave remaining morsels in heavy-duty plastic bag on medium-high power for 30-45 seconds; knead. Microwave at additional 10-20 second intervals, kneading until smooth, Cut tiny corner from bag; squeeze to drizzle over brownies. Chill for 5 minutes. Cut into squares.