For the crust: Preheat your oven to 350°F (175°C). Gently melt 4 tablespoons of butter until smooth. In a medium bowl, combine the finely crushed chocolate wafer cookies with the melted butter. If adding Cognac, stir it in now. Press this mixture firmly into the bottom and evenly up the sides of a standard pie pan. Bake for just 10 minutes until lightly set, then remove from the oven and cool completely on a wire rack.
For the chocolate-caramel filling: Place your finely chopped bittersweet chocolate in a large, heatproof bowl and set it aside. In a separate medium bowl, whisk together the egg yolks, 2/3 cup of the brown sugar, cornstarch, and salt until smooth and light.
In a medium saucepan, gently heat 1/2 cup plus 2 tablespoons of the heavy cream, all of the whole milk, and the remaining 4 tablespoons of butter over medium-high heat until it just begins to simmer around the edges.
Carefully, while continuously whisking, slowly pour about half of the hot milk mixture into the egg mixture to temper it, then return this combined mixture to the saucepan. Continue to whisk gently over medium heat until the pudding thickens and comes to a boil, then cook for one more minute, still whisking. Remove from heat and stir in 1 teaspoon of the vanilla extract.
For the smoothest texture, strain this warm pudding directly over the chopped chocolate. Let it sit undisturbed for 2 minutes, then gently fold the melting chocolate into the pudding with a spatula until beautifully smooth and uniform. Let this luxurious filling cool down to room temperature.
To assemble the pie: Pour a thin, even layer of your favorite caramel sauce into the bottom of the cooled pie crust and refrigerate for 10 minutes. Then, gently spread the cooled chocolate pudding evenly over the caramel. Refrigerate the pie for at least 2 hours, or until firmly set.
For the topping: In a large bowl, combine the remaining heavy cream (about 1.5 cups), 2 tablespoons of brown sugar, 1/2 teaspoon of vanilla extract, and the cocoa powder. Beat with an electric mixer until soft, yet firm peaks form. Carefully spoon or pipe this airy topping over your chilled chocolate filling.
For best results and a truly memorable treat, chill for another 30 minutes, or up to 6 hours before serving.