Preheat the oven to 350 degrees. Cut a piece of parchment paper to fit inside a 16-inch round cake pan and place inside. Grease the bottom and sides of the pan with butter. Dust with flour and tap out any excess. Set aside. Sift the flour, baking soda and salt into a bowl. Set aside. Combine the cocoa and the warm water in a medium sized bowl, whisk until smooth. In another medium sized bowl whisk the buttermilk, water and vanilla, set aside. Add the softened butter to the bowl of a standard mixer. Add the white sugar and the light brown sugar, beat with the paddle until very light in color and texture, about 3 minutes. Scrape the sides of the bowl with a spatula. Break 4 eggs into a small bowl. On low speed, add 1 egg at a time to the bowl. Add the additional eggs only after each is well combined. Scrape the bowl with a spatula. Raise the speed to medium, beat 1-minute until light and fluffy. Add the cocoa mixture, beat on low speed until just combined. Add the flour mixture and the buttermilk mixture alternately: 3 additions of flour, 2 of the buttermilk. I do this visually, a little more than 1 cup of flour, then about 1 cup of the buttermilk mixture, then repeating. Remember to scrape the sides of the bowl with a spatula after each addition. The batter will be smooth. Gently fold in the grated chocolate. Pour the batter into the prepared pan. Bake in the center of the oven until done, about 45 minutes. Do not over bake, the cake will fall firm in the center. Cool. Turn the cake over onto your work surface. Peel off the parchment paper. Cut the cake in half horizontally with a serrated knife. Fill the cake with Chocolate Cream Filling. Top the cake with Thick and Rich Chocolate Glaze.
Chocolate Cream Filling:
Warm the heavy cream in a heavy stainless pot. Add the chopped chocolate and butter. Stir over low heat until the chocolate is almost melted. Take off the heat, and stir until smooth. Cool, then refrigerate until cold. Whip until light and fluffy. Place the bottom layer of the devil's food cake on a cardboard cake circle. Top with the cream filling. Place the other cake layer on top. Press down gently with your hands. Finish the cake with the Thick and Rich Chocolate Glaze.
Thick and Rich Chocolate Glaze:
Warm with heavy cream, in a heavy stainless pot until warm. Add the chopped chocolate and the butter. Stir over low heat until the chocolate is almost melted. Take off the heat and stir until smooth. Cool slightly. Whisk and pour over the filled cake when it has slightly thickened. Smooth with a spatula. For a perfect finish, refrigerate the cake with one coat of glaze on top. When cold and set, add another portion of glaze and smooth nicely with a spatula. Make sure that the second coat of glaze has not hardened. If so, reheat only for a few seconds to the desired consistency.