Preheat the oven to 325°F / 165°C and mix the chocolate cookie crumbs with melted butter, then press into the bottom of a 9-inch springform pan.
Beat the cream cheese and sugar until smooth, then add the melted dark chocolate, eggs, and vanilla extract, mixing until fully combined.
Pour the chocolate cheesecake mixture over the crust and bake for 55 to 60 minutes until the edges are set but the center still jiggles slightly.
Cool the cheesecake to room temperature, then refrigerate for at least 4 hours or overnight until fully chilled.
Spread the whipped cream evenly over the chilled cheesecake to create the mousse layer.
Slice with a warm knife and serve chilled for the cleanest restaurant-style presentation.