Step 1: Preheat oven to 350°F (175°C). Lightly grease a 9×13 inch baking dish (or a 9-inch springform pan). For the crust, combine crushed chocolate cookies and melted butter in a medium bowl. Press firmly into the bottom of the prepared dish. Bake for 8-10 minutes. Let cool completely on a wire rack.
Step 2: Reduce oven temperature to 325°F (160°C). For the cheesecake filling, in a large bowl, beat room temperature cream cheese until smooth. Gradually add granulated sugar, beating until well combined. Beat in eggs one at a time, just until incorporated. Stir in vanilla extract. Pour the cheesecake mixture over the cooled crust.
Step 3: Bake for 45-55 minutes, or until the edges are set and the center slightly jiggles when gently shaken. Turn off the oven, crack the door open slightly, and let the cheesecake cool in the oven for 1 hour. Remove from oven and cool completely on a wire rack, then refrigerate for at least 2 hours.
Step 4: For the milk chocolate mousse, melt milk chocolate chips in a heatproof bowl set over a saucepan of simmering water (or microwave in 30-second intervals), stirring until smooth. Let cool slightly. In a separate cold bowl, whip 1 cup of heavy cream until stiff peaks form. Gently fold the cooled melted milk chocolate into the whipped cream until no streaks remain. Spread evenly over the chilled cheesecake layer. Refrigerate for at least 1 hour to set.
Step 5: For the dark chocolate mousse, repeat the process from Step 4. Melt dark chocolate, let cool slightly. Whip the remaining 1 cup of heavy cream to stiff peaks. Gently fold the cooled melted dark chocolate into the whipped cream. Spread evenly over the set milk chocolate mousse layer. Refrigerate for at least 4 hours, or preferably overnight, until thoroughly chilled and set.
Step 6: To serve, remove from the refrigerator. If using a springform pan, carefully remove the sides. If using a baking dish, run a sharp, hot knife along the edges, then slice into desired portions. Dip the knife in hot water and wipe clean between each slice for clean cuts. Garnish with white chocolate curls before serving. Enjoy!