In a medium mixing bowl, combine the Oreo cookie crumbs and the butter. Pour the mixture into a 9-inch springform pan and use a spoon or the flat bottom of a cup (or measuring cup) to gently press the crust onto the bottom of the pan and about halfway up the sides.

Cover the pan with plastic wrap and chill the crust in the freezer while you prepare the filling.

In a small microwave safe bowl, heat the chocolate chips in the microwave on high for 30 seconds. Stir well then continue microwaving in 20 second intervals until melted; set aside.

In a large mixing bowl, beat the cream cheese, granulated sugar, cocoa powder, and vanilla extract together with an electric mixer until smooth. Stir in the melted chocolate then once combined, fold in half of the Cool Whip.

Spoon the cheesecake filling into the prepared Oreo crust and spread out evenly.

Top the cheesecake with the remaining Cool Whip.

Refrigerate the cheesecake for at least 4 hours.

Use a vegetable peeler to make chocolate curls from the chocolate bar, then sprinkle the curls over the top of the cheesecake.

Remove the outer rim of the springform pan, then slice and serve the cheesecake chilled.