Combine granulated sugar, cornstarch, and salt in a medium saucepan. Whisk in milk and 2 tablespoons espresso powder, and cook over medium-high heat, stirring constantly, until bubbling and thick, about 7 minutes total (about 2 minutes after it comes to a boil).
Whisk yolks in a medium bowl until combined. Pour in milk mixture in a slow, steady stream, whisking until completely incorporated. Return mixture to saucepan, and cook over medium heat, stirring constantly, until it returns to a boil, 1 to 2 minutes.
Remove from heat, and stir in coffee liqueur and vanilla. Add butter, 1 tablespoon at a time, whisking until butter melts before adding next piece. Let custard cool in saucepan on a wire rack, whisking occasionally, for about 10 minutes.
Pour custard into chocolate-wafer crust. Press plastic wrap directly on surface of custard. Refrigerate until custard filling is chilled and firm, at least 4 hours (or overnight).
With a flat side of a chef's knife, crush espresso beans, 1 at a time. Reserve 1 tablespoon larger espresso-bean pieces.
Whisk together cream, confectioners sugar, and remaining teaspoon espresso powder until stiff peaks form. Fold small espresso-bean pieces into whipped cream mixture, and decoratively spread over pie. Sprinkle with reserved espresso-bean pieces, and serve immediately.