1. For crust: In a food processor fitted with a metal blade, pulse cookies until finely ground. Add butter and process until mixture resembles wet sand.

2. Transfer crumb mixture to prepared pie plate, pressing into bottom and up side of pan.

3. Chill crust until firm. Fill with prepared or cooked filling or, alternatively, bake crust in preheated 350F oven for 10 to 15 minutes or until crust is set and fragrant.

4. For filling: In a heavy saucepan, whisk together sugar, cornstarch, salt and egg yolks until well combined. Add 1/2 cup of the milk, whisking well. Whisk in remaining milk and cream. Bring to a simmer over medium heat, whisking. Reduce temperature and simmer, whisking, for 1 minute or until filling is very thick. Remove from heat and whisk in bittersweet and unsweetened chocolate and vanilla.

5. Strain filling through a fine-mesh sieve into a bowl and press a piece of plastic wrap directly onto the surface to prevent a skin from forming. Let cool completely.

6. Stir filling and spread in crust. Chill, loosely covered, for at least 6 hours.

7. For topping: Just prior to serving pie, in a bowl, using an electric mixer or whisk, whip together cream, confectioner's sugar and vanilla until soft peaks form. Swirl whipping cream over top of pie and garnish with chocolate shavings, if desired.