5ounces(142g)semisweet or bittersweet chocolate, finely chopped
For the topping:
1cupchilled heavy cream
3tablespoonspowdered sugar
¼teaspoonrum extract, optional
½teaspoonvanilla extract
Natural unsweetened cocoa powder
Instructions
Preheat oven to 350° F. Pulse cookies in a food processor or blender until finely ground. Drizzle in butter and cream; pulse until well blended. Pour into prepared dish. Use the bottom and sides of a measuring cup to pack crumbs onto bottom and up sides of dish. Bake until crust is set, 12–15 minutes. Let cool completely on a wire rack; set aside.
For the custard, in a small bowl, pour 2 tablespoons water and sprinkle the gelatin over the top. Let the mixture stand until the gelatin softens, about 10 minutes. Meanwhile, heat the milk and cream in a large saucepan over medium heat until mixture just comes to a simmer.
In a medium bowl, whisk egg yolks, sugar, rum extract (if using), cornstarch, vanilla extract and pinch of salt. Whisking vigorously, pour 1/2 cup or so of the hot milk into the egg mixture and rapidly combine. Pour the tempered egg mixture into the pot of hot milk, whisking quickly the entire time. Whisk in the softened gelatin. Place the pan over medium-low heat and whisk the mixture constantly until thick, about 5 minutes.
Remove the vanilla custard from the heat and stir in the mascarpone (if desired, strain the mixture through a fine mesh strainer to remove any lumps or cooked bits of egg). Measure out 1 cup of the custard and place it in a medium bowl. Add the chopped chocolate and lightly stir. Let the mixture sit for 2-3 minutes then stir until the chocolate is melted and the mixture is smooth. Pour the chocolate custard into the cooled crust; smooth the top. Chill the pie until set, about 30 minutes, while letting the vanilla custard stand at room temperature. If the vanilla custard starts to form a skin, lightly press a piece of plastic wrap to the surface.
Gently pour the remaining vanilla custard over the chilled chocolate layer. Pour slowly so the chocolate layer doesn't get messed up. Smooth the top; chill until set, about 1 hour, or keep covered up to 1 day.
When ready to serve, use an electric mixer at medium speed and beat the cream and powdered sugar in a medium bowl until the cream begins to thicken. Add the rum extract and vanilla; increase the speed to high and beat until stiff peaks form. Spread whipped cream over custard. Dust with cocoa powder. Cut into slices and serve (the topped pie can be made 4 hours ahead - chill uncovered).
Notes
Rum Flavor: the rum extract is optional but adds a delicious depth of flavor to the pie. If you aren't sure about using it or don't want a strong rum flavor, start with just a few drops of the extract and go up from there if you want a more pronounced flavor.