1Heat oven to 350ºF. Grease square pan, 8x8x2 inches. In medium bowl, beat granulated sugar, 1/2 cup butter, the vanilla and eggs with electric mixer on medium speed, or stir with spoon. Stir in flour, cocoa, baking powder and salt. Spread in pan.
2Bake 25 to 30 minutes or until toothpick inserted in center comes out clean; cool 15 minutes. Mix remaining ingredients except chocolate; spread over brownies. Refrigerate 15 minutes.
3In 1-quart saucepan, heat chocolate over low heat until melted; spread evenly over powdered sugar mixture. Refrigerate at least 3 hours. For bars, cut into 5 rows by 5 rows; cut each bar diagonally in half to form triangles.