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1
Whisk together granulated sugar, cornstarch, and salt in a medium saucepan.
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2
Whisk in milk and 2 tablespoons 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).
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3
Whisk egg yolks in a medium bowl until combined.
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4
Whisk in milk mixture in a slow, steady stream until completely incorporated.
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5
Return mixture to saucepan, and cook over medium heat, stirring constantly, just until it returns to a boil, 1 to 2 minutes.
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6
Strain through a fine sieve into a large bowl, and stir in coffee liqueur and vanilla.
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7
Add butter, 1 tablespoon at a time, whisking until each piece melts before adding the next one.
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8
Let custard cool, whisking occasionally, about 10 minutes.
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9
Pour custard into baked and cooled crust.
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10
Press plastic wrap directly on surface of custard.
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11
Refrigerate until filling is firm, 4 hours (or, wrapped tightly with plastic, up to 1 day).
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12
With a flat side of a chefs knife, crush espresso beans, 1 at a time.
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13
Reserve 1 tablespoon larger pieces for garnish.
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14
In a chilled bowl, beat cream, confectioners sugar, and remaining 1 teaspoon espresso powder until stiff peaks form.
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15
Fold small espresso-bean pieces into whipped cream mixture, and spread over pie.
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16
Sprinkle with reserved espresso-bean pieces, and serve immediately.
