How to Make It
In a food processor, pulse the 1 1/4 cups of flour with 1/4 teaspoon of salt. Add the butter and pulse until pea-size pieces form. Drizzle in the ice water and pulse until the crumbs are moistened. Turn the dough out onto a work surface and gather it into a ball. Flatten into a disk, wrap in plastic and refrigerate for 30 minutes.
On a floured work surface, roll out the chilled dough to an 11-inch round, a scant 1/4 inch thick; ease it into a 9-inch glass or ceramic pie plate. Trim the overhanging dough to 1 inch and fold it under itself. Crimp decoratively and chill the crust until very firm, about 30 minutes.
Preheat the oven to 350°. Line the crust with parchment paper and fill with pie weights or dried beans. Bake in the lower third of the oven for about 35 minutes, until the crust is set and lightly golden brown. Remove the parchment and pie weights and bake for about 15 minutes more, until golden brown. Transfer the crust to a wire rack and let cool completely.
In a small microwave-safe bowl, heat 2 tablespoons of the heavy cream until steaming, about 30 seconds. Add 2 ounces of the chopped bittersweet chocolate and let stand for 5 minutes, then stir with a rubber spatula until smooth. Pour into the cooled crust and refrigerate until the ganache is firm, about 15 minutes.
In a medium saucepan, heat the milk with 1/4 cup of the granulated sugar over moderate heat until bubbles form around the edge, about 5 minutes. In a large heatproof bowl, whisk the egg yolks with the brown sugar, cornstarch, cocoa powder and ¼ teaspoon of salt. Gradually whisk in the hot milk mixture. Pour this mixture into the saucepan and cook over moderately low heat, whisking constantly, until very thick, about 3 minutes. Remove from the heat and whisk in the remaining 4 ounces of bittersweet chocolate along with the unsweetened chocolate and vanilla until smooth. Strain the chocolate filling over the chilled ganache in the pie crust through a coarse sieve and smooth the surface with a rubber spatula. Press a piece of plastic wrap directly onto the surface of the filling and refrigerate for at least 3 hours, until chilled.
In a medium bowl, using a hand mixer, beat the remaining 2 cups of heavy cream and 2 teaspoons of granulated sugar at medium speed until firm peaks form. Remove the plastic wrap from the chilled pie and spread the whipped cream on top. Refrigerate until the whipped cream is set, about 30 minutes. Garnish with bittersweet chocolate curls and serve.