• Combine the Oreo baking crumbs and melted butter until moistened and crumbly.
• Press the mixture into the bottom of a 9-inch springform pan and refrigerate to set.
• Combine the cream cheese and powdered sugar in a large bowl, mixing with a hand mixer on medium speed (or in your stand mixer) until smooth. 
• Add the Baileys and mix well until incorporated.
• Add the melted white and semi-sweet chocolate in a steady stream while the mixer is running on low speed, until completely incorporated. Scrape down the sides of the bowl to be sure everything is incorporated.
• Fold in the whipped cream or whipped topping by hand until the mixture is fluffy and creamy and there are no streaks of white in the batter.
• Pour the cheesecake mixture into the prepared crust and smooth out the top with a rubber spatula. 
• Refrigerate to set for 6 hours or overnight, or set in the fridge for 2-3 hours and then in the freezer for 2-3 hours before serving, or set in the freezer only for 4 hours.

For decorating:

• Melt the semi-sweet chocolate in the microwave on 50 percent power for 30-second increments until melted.
• Whisk the 3/4 cup plus 2 teaspoons of heavy cream into the melted chocolate until a ganache forms.
• Drizzle the ganache over the chilled cheesecake.
• Top with whipped cream and chocolate shavings, then serve.