Line a 9-inch springform pan with parchment paper. Blend 24 Oreo cookies into fine crumbs, then mix with 5 tablespoons of melted unsalted butter until well combined. Press this mixture into the bottom of the prepared pan and chill for 15 minutes.

Preheat oven to 140°C (285°F). In a large bowl, beat 16 ounces of cream cheese and 1 cup of sour cream until smooth. Mix in 1 cup of caster sugar, zest of 1 orange, 1/4 cup of orange juice, and 1 teaspoon of vanilla extract. Incorporate 3 large eggs one at a time.

Pour the filling over the crust and bake for 60 to 70 minutes until edges are set but center jiggles. Turn off oven, crack door open, and cool cheesecake inside for 1 hour.

Allow cheesecake to sit at room temperature for 30 minutes, then cover and refrigerate for at least 2 hours, preferably overnight.

Chop 8 ounces of dark chocolate and place in a heatproof bowl. Heat 1 cup of heavy cream until simmering and pour over chocolate. Let sit then stir until smooth.

Pour ganache over the chilled cheesecake, allowing it to cascade down the sides. Decorate with orange slices or chocolate segments.