Creating the decadent Oreo Mousse Cake involves several straightforward steps to ensure your dessert turns out amazing. Follow these instructions carefully:

1. Preheat Oven: Preheat your oven to 350°F (175°C).
2. Prepare the Crust: In a food processor, crush the Oreo cookies until fine crumbs form. Mix the crumbs with melted butter until well combined.
3. Form the Crust: Press the cookie mixture firmly into the bottom of a 9-inch springform pan to create an even layer. Bake for about 10 minutes and then allow to cool.
4. Make the Mousse: In a large mixing bowl, beat the heavy whipping cream until soft peaks form. Gradually add powdered sugar and vanilla extract while continuing to beat until stiff peaks form.
5. Combine Cream Cheese Mixture: In another bowl, beat the softened cream cheese and cocoa powder until smooth and well-integrated.
6. Fold Mousse into Mixture: Gently fold the whipped cream into the cream cheese mixture until fully combined, using a spatula to ensure a light and airy texture.
7. Add Chopped Oreos: Carefully fold in the chopped Oreos for added texture and flavor.
8. Layer Mousse in Pan: Pour half of the mousse mixture over the cooled crust in the springform pan and smooth the top with a spatula.
9. Add Second Layer: Pour the remaining mousse mixture on top of the first layer and smooth the surface.
10. Chill in Refrigerator: Cover the pan with plastic wrap and place it in the refrigerator for at least 4 hours, or overnight if you have the time.
11. Prepare for Serving: Once set, carefully remove the sides of the springform pan. Garnish with crushed Oreos and chocolate shavings or drizzles as desired.

Following these steps will lead you to a masterpiece of a dessert that will surely be the star of any gathering.