- With the rack in the middle position, preheat the oven to 180 °C (350 °F). Butter a 20-cm (8-inch) springform pan.
- In a bowl, combine the crumbs and sugar. Add the butter and stir until the crumbs are completely moistened. Press the crumb mixture at the bottom and up to half the edges of the pan. Bake for 12 minutes. Let cool.
- In a saucepan off the heat, combine the sugar and cornstarch with a whisk. Add the eggs and egg yolks, and whisk until smooth. Add the milk and coffee.
- Bring to a boil, whisking constantly, taking care to scrape the sides and bottom of the pan. Simmer for 1 minute. Remove from the heat.
- Add the chocolate and whisk until the cream is smooth. Pour into the crust.
- Cover with plastic wrap directly over the filling and refrigerate for 4 hours or until the filling is completely chilled.
- In a small bowl, place the chocolate. Add the hot coffee. Whisk until the chocolate is melted and smooth. Refrigerate while preparing the remaining ingredients.
- In a bowl, whip the cream, mascarpone and icing sugar until stiff peaks form. With a spatula, gently fold in the chocolate and coffee mixture. Spread over the cooled pie.
The pie will keep for 3 to 4 days in the refrigerator.
Just like whipping cream, mascarpone must be cold when whipped; otherwise it will curdle and split.