Make the crust: Crush the chocolate cookies into fine crumbs. Mix with melted butter and optional sugar until evenly moistened
Press into the dish: Firmly press the crumb mixture into the bottom and slightly up the sides of a 9-inch pie dish. Refrigerate for 20 minutes
Prepare the peanut butter filling: Beat the softened cream cheese and peanut butter until smooth. Add powdered sugar and vanilla, then mix until creamy.
Whip the cream: In a separate bowl, whip 1/2 cup heavy cream until soft peaks form. Gently fold it into the peanut butter mixture.
Fill the crust: Spread the peanut butter mixture evenly over the chilled crust. Refrigerate while preparing the chocolate mousse
Melt the chocolate: Place the chopped chocolate in a heatproof bowl. Warm the milk until hot but not boiling, pour it over the chocolate, and let it stand for 2 minutes. Stir until smooth, then mix in the vanilla
Whip the mousse cream: Beat 1 cup cold heavy cream with 2 tablespoons powdered sugar until medium to stiff peaks form
Combine the mousse: Once the chocolate mixture has cooled to warm or room temperature, gently fold it into the whipped cream until smooth and fluffy.
Layer the mousse: Spoon the chocolate mousse over the peanut butter layer and smooth the top
Chill: Cover and refrigerate for at least 4 hours, preferably overnight.
Add the topping: Whip the remaining heavy cream with powdered sugar and vanilla. Spread or pipe it over the chilled pie.
Garnish and serve: Finish with chocolate shavings or chopped peanut butter cups. Slice with a warm, dry knife for cleaner layers
