Preheat your oven to 350°F (175°C) and lightly spray a 9-inch deep pie dish with cooking spray. In a food processor, blend Oreo cookies and melted unsalted butter until finely crushed and mixed. Press this mixture into the bottom and up the sides of the pie dish. Bake for 10 minutes until fragrant and set; then, let it cool completely on a wire rack.

In a medium saucepan over medium-low heat, whisk together granulated sugar and fresh large eggs. Cook while stirring until the mixture reaches 160°F (71°C), ensuring it thickens slightly. Remove from heat and stir in melted bittersweet chocolate and pure vanilla extract. Allow the chocolate mixture to cool until it reaches around 75°F (24°C).

Using a stand mixer or electric hand mixer, beat the cooled unsalted butter until fluffy and pale, about 2-3 minutes. Gradually mix in the cooled chocolate mixture until smooth.

In a separate bowl, beat heavy cream until stiff peaks form, about 3-5 minutes. Gently fold whipped cream into the chocolate mixture using a spatula.

Pour the rich chocolate filling into the cooled Oreo crust, smoothing the top with a spatula. Cover the pie loosely with plastic wrap and chill in the refrigerator for at least 6 hours.

Before serving, whip additional heavy cream with powdered sugar and vanilla extract until soft peaks form. Spread over the pie and garnish with chocolate shavings or cocoa powder.