To make the crust: Preheat the oven to 350 degrees F. In a food processor, pulse wafers until finely ground. Add 5 tablespoons of butter, 3 tablespoons sugar, and salt, and process until well combined. Press mixture firmly into bottom and up sides of a 9-inch pie plate. Bake until crust is firm, about 10 minutes. Let cool completely on a wire rack. Crust can be stored up to 1 day.
To make the filling: Whisk together granulated 3/4 cup sugar, cornstarch, and salt in a medium saucepan. Whisk in milk and 2 T. espresso powder, and cook over medium-high heat, stirring constantly, until bubbling and thick, about 7 minutes (about 2 minutes after it comes to a boil).
Whisk eggs in a medium bowl until combined. Whisk in milk mixture in a slow, steady stream until completely incorporated. Return mixture to saucepan, and cook over medium heat, stirring constantly just until it returns to a boil, 1 to 2 minutes.
Strain through a fine sieve into a large bowl, and stir in coffee liqueur and vanilla. Add butter, 1 T. at a time, whisking until each piece melts before adding the next one. Let custard cool, whisking occasionally, about 10 minutes.
Pour custard into baked and cooled crust. Press plastic wrap directly on surface of custard (this will prevent it from forming a skin). Refrigerate until filling is firm, overnight is best.
Roughly chop espresso beans. Reserve 1 T. larger pieces for garnish.
In a chilled bowl, beat cream, confectioners' sugar, and remaining 1 teaspoons espresso powder until stiff peaks form. Fold small espresso bean pieces into whipped cream mixture, and spread over pie. Sprinkle with reserved espresso-bean pieces, and serve immediately.