Preparation

Make the ganache layer

• Put the chocolate in a small bowl. Put the cream and cane syrup in a small saucepan over medium heat, and bring to a
  boil. Pour over the chocolate, let sit for 1 minute, and then gently stir with a whisk to blend. Scrape into the cooled pie crust and spread evenly. Freeze the ganache and crust while making the filling.

Make the filling

• Put the sugar, cocoa, cornstarch, espresso powder, and salt in a medium saucepan and whisk until well blended. Pour in 2/3 cup of the milk, and whisk until the mixture is smooth. Whisk in the yolks, and then the remaining milk.
• Set the pan over medium-high heat and cook, stirring with a whisk, until the mixture comes to a full boil. Cook, whisking constantly, for 1 minute, and then slide the pan off the heat. Add the butter and vanilla, and stir until the butter is melted and the pudding is smooth.
• Pour the filling over the chilled ganache layer, spread evenly, and press a piece of plastic wrap directly on the surface to prevent a skin from forming, if you like. Refrigerate until chilled and firm, about 5 hours.

Whip the topping

• Put the heavy cream, mascarpone, sugar, espresso powder, vanilla, and salt in the bowl of a stand mixer fitted with the whisk attachment. Beat on low speed until smooth. Increase the speed to medium, and beat until the cream is thick and holds relaxed peaks.
• Peel off the plastic from the filling. Spread the topping over the filling, or drop in large dollops. If you like, sprinkle with cocoa powder, chocolate curls, or chocolate shards. Serve immediately, or cover loosely and refrigerate for up to 8 hours.