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 melted 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 refrigerated 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.
Slice and serve with whipped cream, chocolate shavings, and fresh berries, if desired.