MAKE THE CRUST
1-Preheat your oven to 350°F (175°C): Preheat your oven to 350°F (175°C).
2-Crush the chocolate sandwich cookies in a: Crush the chocolate sandwich cookies in a food processor until fine crumbs form.
3-Add the melted butter and pulse until: Add the melted butter and pulse until the mixture resembles wet sand.
4-Press the mixture firmly into the bottom: Press the mixture firmly into the bottom and up the sides of a 9-inch pie dish, using the bottom of a glass or measuring cup to compact it tightly.
5-Bake for 8-10 minutes, then let it: Bake for 8-10 minutes, then let it cool completely.

PREPARE THE FUDGE LAYER
6-In a heatproof bowl, melt the chocolate: In a heatproof bowl, melt the chocolate chips and heavy cream together over a double boiler or in the microwave in 20-second increments, stirring until smooth.
7-In a separate bowl, whisk together the: In a separate bowl, whisk together the sugar and eggs until well combined.
8-Slowly pour the melted chocolate mixture into: Slowly pour the melted chocolate mixture into the egg mixture, whisking constantly.
9-Stir in the vanilla extract: Stir in the vanilla extract.
10-Pour the fudge mixture over the cooled: Pour the fudge mixture over the cooled crust and bake at 325°F (163°C) for 15-18 minutes, until the edges are set but the center is slightly wobbly.
11-Cool completely: Cool completely.

MAKE THE CHOCOLATE MOUSSE LAYER
12-Melt the chocolate chips with ½ cup: Melt the chocolate chips with ½ cup of heavy cream in the microwave or over a double boiler, stirring until smooth.
13-Let it cool slightly: Let it cool slightly.
14-Whip the remaining 1 cup of heavy: Whip the remaining 1 cup of heavy cream with the powdered sugar until stiff peaks form.
15-Gently fold the whipped cream into the: Gently fold the whipped cream into the cooled chocolate mixture.
16-Spread the mousse evenly over the cooled: Spread the mousse evenly over the cooled fudge layer.
17-Chill in the refrigerator for at least: Chill in the refrigerator for at least 3 hours, or until set.

WHIPPED CREAM TOPPING
18-Whip the heavy cream, powdered sugar, and: Whip the heavy cream, powdered sugar, and vanilla extract together until stiff peaks form.
19-Spoon or pipe the whipped cream over: Spoon or pipe the whipped cream over the chocolate mousse layer.
20-For a decorative finish, use a piping: For a decorative finish, use a piping bag fitted with a star tip.

ADD THE FINISHING TOUCHES
21-Decorate the top with chocolate shavings, curls,: Decorate the top with chocolate shavings, curls, or pieces.
22-Lightly dust the top with cocoa powder,: Lightly dust the top with cocoa powder, if desired, for a polished look.