In a medium bowl, combine Oreo baking crumbs and melted butter until the mixture is crumbly and moist.
Press the Oreo mixture into the bottom of a springform cheesecake pan (a 9-inch pan) and place in the fridge to chill.
Add the cream cheese to a large bowl and mix with a hand mixer (or use your stand mixer) until creamy and smooth.
Sift the powdered sugar to remove lumps and add it to the cream cheese, mixing on medium speed until incorporated.
Melt the chocolate by using a double boiler (a heat-safe bowl over a pot of simmering water) or in the microwave at 50% power for 30-second increments until the chocolate is completely melted and smooth.
Let the chocolate cool to room temperature and add it to the cream cheese mixture in a steady stream while the mixer is running.
Fold the whipped topping gently into the cheesecake mixture until everything is incorporated.
Pour the filling on top of the Oreo crumb base and place in the fridge for 6 hours, or overnight. Alternatively, chill in the fridge for 2 hours and in the freezer for 2 hours to set.
Slice and serve with chocolate shavings, whipped cream and chocolate sauce, if desired.
Feel free to substitute real whipped cream for whipped topping. Simply add an additional 1/4 cup of powdered sugar in this case.