Preheat the Oven: Begin by preheating your oven to 325°F (160°C).
Prepare the Crust: Crush the Oreo cookies in a food processor until they resemble fine crumbs. Mix the crumb with melted butter until well combined, then press the mixture firmly into the bottom of a springform pan to form the crust.
Mix the Cheesecake Filling: In a large mixing bowl, beat the softened cream cheese with sugar until creamy and smooth.
Incorporate Chocolate: Pour in the melted dark chocolate and mix thoroughly until there's no streaks.
Add Eggs: Add the eggs one at a time, mixing well after each addition, followed by the vanilla extract.
Bake the Cheesecake: Pour the cheesecake mixture over the prepared crust and smooth the top. Bake in the preheated oven for 55-60 minutes or until the center is set but still slightly jiggly.
Cool: Remove the cheesecake from the oven and let it cool on a wire rack. Once cooled, spread sour cream over the top.
Chill: Place the cheesecake in the refrigerator to chill for at least 4 hours or overnight before serving.