Preheat oven to 350°F (180°C). Grease and flour 2 (9-inch/29 cm) round cake pans. Mix boiling water and cocoa powder in medium bowl with wire whisk until well blended. Add chopped chocolate; mix well. Let stand 20 minutes or until cooled; stirring occasionally. Stir in vanilla. Set aside. Mix flour, baking soda, baking powder and salt in medium bowl. Set aside.