Black Bottom Pie

Preheat oven to 350°. Pulse cookies in a food processor 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.

Pour 2 Tbsp. water into a small bowl; sprinkle gelatin over. Let stand until gelatin softens, about 10 minutes. Heat milk and cream in a large saucepan over medium heat until mixture just comes to a simmer.

Whisk egg yolks and next 5 ingredients in a medium bowl. Gradually whisk egg mixture into milk mixture; whisk in gelatin. Whisk constantly over medium-low heat until thick, about 5 minutes.

Remove vanilla custard from heat and stir in mascarpone. Place 1 cup custard in a medium bowl; add chocolate and stir until melted and smooth. Stir in espresso. Pour chocolate custard into crust; smooth top. Chill pie until set, about 30 minutes. Let vanilla custard stand at room temperature.

Gently pour remaining vanilla custard over chilled chocolate layer (pour slowly so as not to disturb chocolate layer). Smooth top; chill until set, about 1 hour, or keep covered up to 1 day.

Using an electric mixer at medium-low speed, beat cream and sugar in a medium bowl until cream begins to thicken. Add rum and vanilla; increase speed to high and beat until stiff peaks form. Spread whipped cream over custard. Dust with cocoa powder and garnish with grated chocolate and almonds. DO AHEAD: Can be made 4 hours ahead. Chill uncovered.