Preheat oven to 350°F. Line a 9-inch square baking pan with non-stick foil. Set aside. Reserve 2 oz. of the chocolate. Chop remaining 6 oz. of chocolate and place in large microwave-safe bowl. Add butter. Microwave 1 min, stir. Microwave 30 seconds, stir until smooth.
Stir sugar, flour, baking soda and salt into chocolate mix until well blended. Add eggs and vanilla. Stir until smooth. Chop remaining 2 oz. chocolate. Stir into batter. Pour into pan, spread evenly.
Bake for 45 min or until toothpick inserted in center comes out clean. Cool for 10 min. Dust with confectioners' sugar.