Creating the Oreo Mousse Cake involves a series of straightforward steps. Follow these instructions for sumptuous results:

1. Prepare the Cookie Crust: In a mixing bowl, combine the crumbled Oreo cookies with melted butter. Mix until the crumbs are evenly coated.
2. Form the Crust: Press the Oreo mixture firmly into the bottom of a 9-inch springform pan. Ensure it is compact and even. Place in the refrigerator to set while preparing the mousse.
3. Make the Mousse: In a large bowl, beat the heavy cream and powdered sugar until stiff peaks form.
4. Combine Cream Cheese and Chocolate: In another bowl, blend the softened cream cheese and melted chocolate until smooth. Add in vanilla extract and mix well.
5. Fold Whipped Cream: Carefully fold the whipped cream into the chocolate mixture until fully combined and smooth.
6. Layer the Mousse: Pour the mousse over the prepared crust in the springform pan. Smooth the top using a spatula.
7. Chill: Cover the pan with plastic wrap and refrigerate for at least 4 hours to allow the mousse to set completely.
8. Prepare Ganache: In a small saucepan over low heat, heat the milk chocolate and heavy cream until melted and smooth, stirring frequently. Allow to cool slightly.
9. Top the Cake: Once the mousse is set, carefully pour the ganache over the top and spread evenly.
10. Decorate: Garnish with additional crushed Oreo cookies on top.
11. Serve: Release the sides of the springform pan to reveal the layered cake. Cut into slices and enjoy!

By following these steps, you will have an incredible Oreo Mousse Cake that will impress anyone!