Heat the oven to 350°F. Combine the chocolate wafer crumbs, melted butter, granulated sugar, and salt until the crumbs are evenly moistened.

Press the crust mixture firmly over the bottom and up the sides of a 9-inch pie plate. Bake for about 10 minutes, then cool the crust completely before adding the filling.

In a saucepan, whisk together the sugar, cornstarch, and salt. Whisk in the milk, cream, egg yolks, and instant espresso powder until the mixture is well blended.

Cook the custard over medium heat, whisking constantly, until it thickens and reaches a gentle boil. Continue cooking for about 1 minute after it thickens, paying close attention to the bottom and edges.

Remove the saucepan from the heat and stir in the vanilla extract. For an especially smooth filling, strain the warm custard through a fine-mesh sieve.

Pour the warm coffee custard into the cooled chocolate crust. Press plastic wrap directly onto the custard surface, then refrigerate the pie until completely set for at least 4 hours, preferably overnight.

Whip the cold heavy cream with the confectioners’ sugar and vanilla until medium-stiff peaks form. Spread or pipe the whipped cream over the chilled pie and finish with chocolate shavings, cocoa powder, or chocolate-covered espresso beans.