Begin by crushing Oreo cookies into fine crumbs using a food processor or a rolling pin. In a medium bowl, mix the crumbs with melted butter until they resemble wet sand. Press this mixture firmly into the bottom of a springform pan, spreading it evenly. Place the pan in the refrigerator to chill for 30 minutes to allow the crust to set.

While the crust chills, melt semi-sweet or dark chocolate in a microwave or double boiler until smooth. Allow it to cool slightly. In a mixing bowl, use an electric mixer to beat room-temperature cream cheese, powdered sugar, and vanilla extract until creamy and free of lumps. Gently fold in the cooled chocolate until thoroughly combined.

In a separate bowl, whip the heavy cream until stiff peaks form. Carefully fold the whipped cream into the chocolate mixture in batches, using a spatula to maintain volume.

Retrieve the chilled crust from the refrigerator and spread the chocolate filling over it, smoothing the top with a spatula. Cover the springform pan with plastic wrap and refrigerate the cheesecake for at least 6 hours, or preferably overnight.

To make the ganache, heat heavy cream in a small saucepan over medium heat until it begins to steam. Pour the hot cream over chopped semi-sweet chocolate in a bowl and let it sit for a few minutes. Stir gently until the mixture is smooth and glossy.

Once the cheesecake has set, drizzle the cooled ganache over the top. Return the cheesecake to the refrigerator to chill for an additional 30 to 60 minutes before serving.