Make a rich, creamy, and light chocolate mousse pie without turning on your oven. This recipe uses a simple Oreo crust and a stabilized whipped cream topping.
Prepare the crust: Combine cookie crumbs, 1/4 cup granulated sugar, and melted butter in a bowl. Press the mixture firmly into the bottom and up the sides of a 9-inch pie plate. Chill the crust for at least 30 minutes.
Melt the chocolate: Place the chopped bittersweet chocolate in a heatproof bowl. Heat 1/4 cup water until simmering, then pour it over the chocolate. Let it sit for 2 minutes, then stir until the chocolate is completely smooth. Stir in the vanilla extract. Let the mixture cool slightly, about 10 minutes.
Make the mousse base: In a separate bowl, beat 1 cup of cold heavy cream with 1/4 cup powdered sugar until medium peaks form.
Fold the chocolate into the cream: Gently fold about one-third of the whipped cream into the slightly cooled chocolate mixture to lighten it. Then, fold the lightened chocolate mixture back into the remaining whipped cream until just combined and no streaks remain. Do not overmix.
Fill the pie: Spoon the mousse filling evenly into the chilled Oreo crust. Smooth the top with a spatula.
Chill the pie: Refrigerate the pie for at least 4 hours, or until the mousse is firm.
Prepare the topping: Just before serving, beat the remaining 1/2 cup cold heavy cream with 1 teaspoon powdered sugar until stiff peaks form. Spread or pipe the whipped cream over the chilled pie.
Garnish: Sprinkle the top with extra chocolate shavings, if desired. Slice and serve cold.
Notes
For a firmer mousse, you can substitute 1 teaspoon of unflavored gelatin dissolved in 2 tablespoons of hot water for 2 tablespoons of the water used to melt the chocolate. Add the dissolved gelatin to the melted chocolate mixture before folding in the whipped cream.
Use high-quality dark chocolate for the best flavor in the mousse.
If you do not have chocolate wafers, you can substitute with Oreo cookies (remove the cream filling first).