Special equipment: a 9 by 3 1/2-inch spring form pan and a large pastry bag
To make the crust: Preheat the oven to 350 degrees F.
Pulse the graham crackers and brown sugar in a food processor to a fine crumb. Melt the butter in a small saucepan, add it to the crumb mixture, and pulse until just combined. Pour the mixture into the spring form pan and press it firmly along the bottom and all the way up the sides of the pan to make an even crust. Bake until the crust browns, about 15 minutes. Cool and refrigerate while making the pudding.
To make the pudding: In a small medium saucepan, melt the butter over medium heat. Whisk in the dark brown sugar and cook, stirring, until melted and bubbly. Gradually add in the heavy cream and stir over low heat until the butterscotch is dissolved. Whisk in the milk and salt. Remove from the heat and set aside until lukewarm. Pour the 2 tablespoons of water into a small bowl and sprinkle the gelatin over the top, do not stir. Set aside to let the gelatin bloom.
In a small bowl, whisk together the cornstarch and the remaining 1/4 cup water. Stir the cornstarch mixture into the butterscotch mixture. Cook, stirring constantly, over medium-high heat until the mixture thickens. Reduce the heat to low; stir briskly, and bring to a simmer and cook for 1 minute. Remove from the heat and stir in the gelatin mixture and vanilla. Whisk until smooth. Cover the surface of the pudding with plastic wrap and store in the refrigerator while you make the ganache.
To make the Ganache: Put the 6 ounces of chocolate in a medium bowl. In a small saucepan, bring the cream and butter to a boil over high heat. Pour the hot cream mixture over the chocolate; set it aside for 5 minutes before whisking until smooth.
Pour the chocolate ganache into the chilled crust; then swirl the pan so the ganache evenly covers the sides and bottom of the crust. Set the crust aside at room temperature while you make the chocolate mousse.
To make the Mousse: Put the 8 ounces of chocolate in a large bowl. In a small saucepan, bring 1/2 cup of the cream, the brandy, and vanilla to a boil over medium high heat. Pour the hot cream mixture over the chocolate; set it aside for 5 minutes before whisking until smooth. Cool the chocolate mixture to room temperature, whisking occasionally.
In a large bowl, beat the remaining 1 1/2 cups cream until it holds a soft peak. Sift the sugar over the cream, and continue beating until slightly thicker; take care not to over whip the cream. Fold a third of the whipped cream into the chocolate to lighten the mixture. Fold in the remaining cream.
To assemble the Parfait Pie: Pour the pudding into the prepared crust and smooth the top with a spatula. Pour the chocolate mousse on top of the pudding, smooth the top if needed. Refrigerate until set, about 6 hours. In a medium bowl whip the cream and brandy until it holds a soft peak. Spoon dollops of the whipped cream over the chocolate to cover and decorate with the chocolate shavings. Carefully remove the spring form ring. Transfer the Parfait Pie to a cake stand and serve. Cut with a warm serrated knife.