Prep the pan and oven: Heat the oven to 325°F (160°C). Wrap the outside of a 9-inch springform pan with two layers of heavy-duty foil to keep water out during baking.

Make the crust: Pulse 9 ounces of chocolate wafer cookies to fine crumbs. Stir in 5 tablespoons melted unsalted butter and a small pinch of salt. Press the mixture firmly into the bottom of the pan. Use the bottom of a measuring cup to pack it tightly.

Par-bake the crust: Bake for 8–10 minutes until set and fragrant. Let it cool on a rack while you make the filling. Reduce oven temperature to 300°F (150°C) for gentler baking.

Melt the chocolate: Gently melt 8 ounces dark chocolate in a heatproof bowl set over barely simmering water, or microwave in short bursts, stirring until smooth. Let it cool slightly so it’s warm but not hot.

Beat the cream cheese: In a large bowl, beat 24 ounces room-temperature cream cheese on medium speed until smooth and fluffy, about 2 minutes. Scrape the bowl often to avoid lumps.

Add sugar and sour cream: Beat in 3/4 cup granulated sugar and 3/4 cup sour cream until fully blended and silky. Mix in 1 teaspoon vanilla and a pinch of salt.

Add orange: Finely zest 2 oranges (about 2 tablespoons zest) directly into the bowl. Add 2 tablespoons fresh orange juice. Mix just to combine. The zest is where most of the orange flavor lives, so don’t skip it.

Add eggs: Beat in 3 large eggs one at a time on low speed, just until incorporated. Avoid overmixing to reduce air bubbles.

Blend in chocolate: With the mixer on low, slowly stream in the melted chocolate. Mix until uniform, then give the bowl a final scrape and gentle stir.

Assemble the water bath: Pour the batter over the cooled crust. Place the foil-wrapped pan in a large roasting pan. Pour hot water into the roasting pan to reach halfway up the sides of the springform.

Bake low and slow: Bake at 300°F for 55–70 minutes. The edges should be set and the center should still wobble slightly when you jiggle the pan. It will firm up as it cools.

Cool gradually: Turn off the oven, crack the door, and let the cheesecake sit inside for 45 minutes. This gentle cool helps prevent cracks.

Chill completely: Remove from the water bath, discard foil, and cool to room temperature. Cover and chill at least 6 hours, preferably overnight, before slicing.

Finish and serve: Warm a few tablespoons of orange marmalade and spread a thin glossy layer on top, if you like. Add whipped cream, chocolate curls, or candied peel. Slice with a hot, clean knife for neat wedges.