For the Chocolate: Combine and boil until thick the butter, chocolate and boiling water. Stirring constantly. Set aside and allow to cool while you mix the other ingredients. In a cup combine the buttermilk and baking soda, set aside. Stir together flour, sugar and salt. Make a well in the center and add chocolate. Mix well and then add the eggs. When the eggs are blended completely then add the buttermilk. Add vanilla last. Grease and flour pans you can use 2, 9" cake pans or one 9x12" pan. Bake in a 350F oven 25-30 minutes for 9" pans or 40 minutes for the 9x12" pan. For the Frosting: Cream butter and cream cheese until smooth. Gradually add powdered sugar. Add vanilla. Add milk as needed to make the frosting spreadable and smooth.