01 - Combine graham cracker or chocolate cookie crumbs with granulated sugar in a medium bowl. Pour in melted butter and stir until evenly moistened. Press mixture firmly into the bottom and up the sides of a 9-inch pie dish. Freeze for 15 minutes to set.
02 - Preheat oven to 350°F. Bake the chilled crust for 10 minutes until lightly golden. Remove from oven and allow to cool completely before filling.
03 - Place chopped chocolate in a heatproof bowl set over a saucepan of barely simmering water, creating a double boiler. Stir continuously until chocolate is completely melted and smooth. Remove from heat and cool to room temperature.
04 - In a large bowl, beat room temperature unsalted butter and sifted powdered sugar with an electric mixer on medium speed for 2 to 3 minutes until the mixture becomes light and fluffy.
05 - Add the cooled melted chocolate and vanilla extract to the butter mixture. Beat on medium speed until thoroughly combined and the mixture is uniform in color.
06 - Add eggs one at a time, beating on medium-high speed for 3 to 5 minutes after each addition. This critical step aerates the filling, creating the signature silky, mousse-like texture.
07 - Spread the chocolate filling evenly into the cooled pie crust, smoothing the top with a spatula. Refrigerate for at least 4 hours or until completely set and firm.
08 - Just before serving, whip together cold heavy cream, powdered sugar, and vanilla extract in a chilled bowl. Beat until soft peaks form that hold their shape.
09 - Spread or pipe the whipped cream over the chilled pie surface. Garnish with chocolate shavings if desired. Slice and serve cold.