Instructions

1. Arrange a rack in the middle of the oven and heat to 375°F. Place 30 chocolate wafer cookies and 1/4 teaspoon kosher salt in the bowl of a food processor fitted with the blade attachment and process into crumbs, about 30 seconds. Remove 2 tablespoons of the crumbs and set aside for topping the pie. Drizzle 6 tablespoons melted unsalted butter over the crumbs still in the food processor and pulse until incorporated, about 10 (1-second) pulses. Transfer to a 9-inch pie plate. Press into an even layer on the bottom and up the sides of the pie plate using your fingers or the bottom of a measuring cup.
2. Place the pie plate on a baking sheet to make it easier to handle. Bake the crust for 10 minutes. Place the pie pan on a wire rack to cool to room temperature.
3. Place 1/4 cup green crème de menthe liqueur and 2 tablespoons white crème de cacao in a large heatproof bowl. Sprinkle 1 (1/4-ounce) envelope unflavored gelatin powder over the liqueurs and set aside until the gelatin swells, about 5 minutes.
4. Using a stand mixer fitted with the whisk attachment or an electric hand mixer or hand whisk and large bowl, whisk 1 1/2 cups cold heavy cream and 2 tablespoons of the sugar to stiff peaks. Cover with plastic wrap and refrigerate.
5. Bring 1 inch of water to a simmer in a medium saucepan. Set the bowl of bloomed gelatin over the simmering water and stir until the gelatin dissolves, about 2 minutes. Remove from the heat.
6. Place the remaining 1/2 cup of sugar, 4 large egg yolks, and 1/2 teaspoon kosher salt in a medium bowl and whisk until lightened in color and thickened. Whisk 1/2 of the egg yolk mixture into the warm gelatin mixture to temper the eggs. Whisk in the rest of the egg yolk mixture, and then set the bowl back over the simmering water. Whisk constantly until the mixture reaches 160°F and coats the back of a spoon, 5 to 7 minutes.
7. Remove the bowl from the heat and set on a kitchen towel. Whisk to cool the mixture slightly (about 110°F), about 5 minutes. Stir 1/2 cup of the whipped cream into the egg mixture to lighten it. Fold in 2 1/2 additional cups of the whipped cream until no white streaks remain.
8. Pour the filling into the cooled crust. Refrigerate until the pie is set, about 2 hours. Cover and refrigerate the remaining whipped cream until you are ready to garnish the pie.
9. Spread the reserved whipped cream on the center of the pie so that the green filling can be seen around the edges. Sprinkle with reserved cookie crumbs, drizzle with chocolate syrup if desired, and serve.