Grease the base and sides of a 9" springform pan and set aside.

Stir together the Oreo crumbs and melted butter until all the crumbs are moist. Press the mixture into the prepared pan and refrigerate while preparing the cheesecake.

Using a handheld or stand mixer fitted with the whisk attachment, whip the heavy cream on high speed until it starts to thicken. Add the icing sugar and vanilla and whip until stiff peeks form.

In a separate bowl, whisk together the cream cheese and sugar until smooth and combined. Add the cooled chocolate, and mix until combined. Gently fold in the whipped cream.

Spread the mixture evenly over the cooled crust and smooth out the top. Refrigerate for at least 6 hours - preferably overnight.

Microwave the chocolate and butter together in 20 second intervals, stirring after each one, until melted and smooth. Leave to cool for 5 minutes. Spread over the cheesecake, and serve!