To prepare the dark chocolate cream, heat 1-inch of water in the bottom half of a double boiler over medium heat. Place the 8 ounces semisweet chocolate broken into pieces in the top half of the double boiler. Tightly cover the top with film wrap and allow to heat for 8 to 10 minutes. Remove from the heat and stir until smooth. Transfer the melted chocolate to a stainless steel bowl and set aside until needed. Place 2 1/2 cups heavy cream and 2 tablespoons sugar in the well-chilled bowl of an electric mixer fitted with a well-chilled balloon whip. Whisk on high until stiff peaks form, about 1 1/2 minutes. Remove the bowl from the mixer. Use a hand whisk to combine 1/4 of the whipped cream into the melted chocolate until smooth and completely incorporated. Add the combined whipped cream and chocolate to the remaining whipped cream and use a rubber spatula to fold together.

Transfer the dark chocolate cream to a stainless steel bowl. Tightly cover the top with film wrap and refrigerate until needed. To prepare the cocoa cream, place 2 cups heavy cream, 1/2 cup sugar, the cocoa and 1/2 teaspoon vanilla extract in the well-chilled bowl of an electric mixer fitted with a well-chilled balloon whip. Mix on medium until stiff peaks form, about 4 to 5 minutes. Transfer the cocoa cream to a stainless steel bowl. Tightly cover the top with film wrap and refrigerate until needed. To prepare the speckled chocolate cream, place the remaining 2 cups heavy cream, 2 tablespoons sugar and 1/2 teaspoon vanilla extract in the well-chilled bowl of an electric mixer fitted with a well-chilled balloon whip. Mix on high until stiff peaks form, about 1 1/4 minutes. Remove the bowl from the mixer and use a rubber spatula to fold in the 4 ounces grated chocolate. Transfer the cream to a stainless steel bowl and refrigerate for at least 30 minutes before assembling the parfaits.

To assemble the parfaits, fill a pastry bag (without a tip) with the dark chocolate cream. Pipe an even layer of about 1/2 cup of the cream into each of the brandy snifters. Then fill a clean pastry bag with the cocoa cream and pipe an even layer of it onto the layer of dark chocolate cream. For the final layer of cream, fill a clean pastry bag with the speckled chocolate cream and pipe an even layer of the cream onto the cocoa cream. Refrigerate the parfaits until just a few minutes before serving.