1. Lightly grease the bottoms and sides of two 9-inch round cake pans with butter and line the bottoms with wax paper, then coat with butter. Microwave the chocolate on high for 1 minute. Stir and microwave another 30 seconds. Stir until the chocolate melts and let cool.
2. Next, in a medium bowl, whisk together 2/3 cup boiling water and the cocoa. Stir in the milk and the vanilla and set aside. In a large bowl, add the brown sugar and the butter. Beat with a mixer at medium speed for 3 minutes or until well-blended. Add the eggs, one at a time, beating well after each addition and stir in the melted chocolate. In another bowl, combine the flour, baking soda and 1/4 teaspoon salt, stirring well with a whisk. Add the flour mixture and cocoa mixture alternately to the egg mixture, beginning and ending with the flour mixture.
3. Pour the batter into the prepared pans and bake at 350°F for 30 minutes or until a wooden pick inserted into the center comes out clean.
To Prepare the Frosting
1. Combine the cream and granulated sugar in a medium saucepan over medium heat. Cook until the sugar melts, stirring frequently. Cook an additional 5 minutes, stirring constantly, but do not boil.
2. Place the chopped chocolate in a large mixing bowl and pour the cream mixture over the chocolate, stirring until the chocolate melts. Add the butter and stir until it melts. Then, stir in the vanilla and the salt. Refrigerate for 30 minutes, or just until cool.
3. Beat with a stand mixer using the whip attachment or a hand mixer at high speed until the mixture thickens to a light, spreadable consistency-about 2 minutes. Frost the cooled cake and decorate to celebrate your special occasion!