In a medium bowl, combine the crushed chocolate cookies with the melted butter. Mix until the crumbs are evenly coated and the mixture resembles wet sand.
Press the mixture firmly into the bottom of a 9-inch (23 cm) springform pan using the back of a spoon or the bottom of a glass. This ensures a compact, sturdy crust that will hold the mousse layers well.
Transfer the crust to the refrigerator to chill while preparing the mousse. This helps it set and prevents crumbs from mixing into the filling.
2️⃣ Make the Peanut Butter Mousse
In a large mixing bowl, beat together the softened cream cheese, peanut butter, powdered sugar, and vanilla extract until smooth and creamy. Scrape down the sides of the bowl to ensure all ingredients are evenly combined.
In a separate chilled bowl, whip the cold heavy cream until stiff peaks form. The cream should be fluffy and hold its shape but still appear silky, not grainy.
Gently fold the whipped cream into the peanut butter mixture in batches. Use a spatula and light folding motions to preserve the airy texture. Continue until the mixture is smooth and uniform.
Pour the mousse over the chilled crust, spreading it evenly and smoothing the top with a spatula. Refrigerate for at least 4 hours, or overnight, to allow the mousse to firm up completely.
