Preheat the oven to 350°F (175°C). In a food processor, pulse the chocolate sandwich cookies into fine crumbs. Add the melted butter and process until the mixture has the texture of damp sand. Firmly press the crumb mixture into the bottom and up the sides of a 9-inch pie dish, using the base of a glass or measuring cup to pack it tightly. Bake the crust for 8–10 minutes, then remove it from the oven and allow it to cool completely.

In a heat-safe bowl, combine the chocolate chips and heavy cream. Melt them together using a double boiler or by microwaving in 20-second intervals, stirring until the mixture is completely smooth. In a separate bowl, whisk the granulated sugar and eggs until well blended. Slowly stream the melted chocolate mixture into the eggs while whisking continuously. Stir in the vanilla extract. Pour the fudge filling over the cooled crust and bake at 325°F (163°C) for 15–18 minutes, until the edges are set but the center is still slightly soft and wobbly. Let it cool completely before adding the next layer.

In a microwave-safe bowl or over a double boiler, melt the chocolate chips with 1/2 cup of the heavy cream, stirring until smooth. Let the mixture cool slightly. In a separate bowl, whip the remaining 1 cup of heavy cream with the powdered sugar until stiff peaks form. Carefully fold the whipped cream into the cooled chocolate mixture until fully combined and fluffy. Spread the mousse evenly over the cooled fudge layer and refrigerate for at least 3 hours, or until the mousse is firm and set.

Whip the heavy cream together with the powdered sugar and vanilla extract until stiff peaks form. Spoon or pipe the whipped cream over the top of the chilled mousse layer. For a more elegant presentation, use a piping bag fitted with a decorative tip such as a star nozzle.

Garnish the pie with chocolate shavings, curls, or chocolate pieces for added texture and appeal. If desired, lightly dust the top with cocoa powder to give it a finished and polished appearance.