PREHEAT oven to 325º F. Grease 8-inch-square baking pan. Set aside 2 ounces chocolate (1/2 bar) for drizzle topping.
HEAT 8 ounces (2 bars broken into small pieces) sugar, butter and water in small saucepan over low heat, stirring constantly, until chocolate and butter are melted. Pour into medium bowl. Stir in eggs, one at a time, until mixed in. Stir in vanilla extract. Add flour and salt; stir well. Stir into nuts, if desired. Pour into prepared baking pan.
BAKE for 33 to 35 minutes until wooden pick inserted in center comes out still slightly sticky. Cool in pan on wire rack.
PLACE reserved 2 ounces of chocolate broken into small pieces, in small, heavy-duty plastic bag. Microwave on MEDIUM-HIGH (70%) power for 20 seconds, knead bag to mix. Microwave at additional 10- second intervals, kneading until smooth. Cut a small hole in corner of bag; squeeze to drizzle over brownie. Cut into bars.