Grease an 8-inch springform pan. Crush biscuits into fine crumbs and mix with orange zest and melted butter. Press firmly into the pan base and chill.

Beat room-temperature cream cheese until smooth. Add both sugars, orange zest, orange juice, and vanilla extract. Beat until combined and smooth.

Beat in the slightly cooled, melted dark chocolate until fully incorporated.

In a separate bowl, whip the cold heavy cream until it holds stiff peaks.

Gently fold the whipped cream into the chocolate-cheese mixture in two additions until no white streaks remain.

Pour the filling over the chilled base, spread evenly, and tap to remove air bubbles. Cover and refrigerate for at least 6 hours, preferably overnight.

For the ganache, pour hot (simmering) cream over finely chopped chocolate. Let sit for 2-3 mins, then whisk until smooth. Let cool slightly until pourable.

Release the cheesecake from the pan. Pour the ganache over the top, spreading to the edges. Garnish and return to fridge for 30 mins to set. Use a hot knife to slice.