Preheat oven to 350°F (175°C).

In a medium bowl, combine the crushed chocolate wafer cookies and melted butter. Mix until well combined.

Press the cookie mixture evenly into the bottom and up the sides of a 9-inch pie plate.

Bake the crust for 8-10 minutes. Let it cool completely on a wire rack.

In a double boiler or a heatproof bowl set over simmering water, melt the bittersweet chocolate chips, stirring until smooth.

Remove from heat and set aside to cool slightly.

In a large bowl, cream together the softened butter and granulated sugar until light and fluffy.

Beat in the eggs, one at a time, until well incorporated. Stir in the vanilla extract.

Gradually beat in the melted chocolate until the mixture is smooth and combined.

In a separate chilled bowl, whip the heavy cream until stiff peaks form.

Gently fold about one-third of the whipped cream into the chocolate mixture to lighten it. Then, carefully fold in the remaining whipped cream until just combined, being careful not to overmix.

Pour the filling into the cooled pie crust and spread evenly.

Cover the pie with plastic wrap and refrigerate for at least 4 hours, or until firm.

Before serving, garnish with additional whipped cream and chocolate shavings, if desired.