Preheat oven to 350°F. Grease and flour 2 (9-inch) 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.
Beat butter and sugars in large bowl with electric mixer on medium speed until light and fluffy. Beat in eggs, 1 at a time. Beat in cocoa powder mixture until well blended. Alternately beat in flour mixture and buttermilk on low speed until just blended. Pour batter into prepared pans.
Bake 25 to 30 minutes or until toothpick inserted in center comes out clean. Cool in pan 10 minutes. Remove from pans; cool completely on wire rack.
For the Frosting, mix confectioners’ sugar, cocoa powder and cinnamon in medium bowl until well blended. Set aside. Beat cream cheese and butter in large bowl with electric mixer on medium speed until smooth. Gradually beat in cocoa mixture on low speed until well blended. Gradually beat in melted chocolate then vanilla until well blended. Fill and frost cake with Frosting.