• Preheat the oven to 350 °F. Line the bottom of a 9"x3" round cake pan or spring form pan with a parchment paper round.

Make the Crust

• Run the 7 oz Oreo cookie crumbs and 2 tablespoons all purpose flour in a food processor or blender to make the crumbs. Add 2 oz unsalted butter (melted) and pulse a few times to combine. Dump the crumbs into the cake pan and press into an even layer. Bake the crust for 10 minutes until fragrant. Reduce the oven temperature to 325 °F.

To make the cheesecake batter

• (If you're using a spring form pan wrap the pan with aluminum foil to cover the bottom and sides.)
• Combine 16 oz cream cheese and 4 oz granulated sugar in a mixing bowl. Mix on medium speed to combine the ingredients, scraping the bowl often to avoid lumps. Once the mix is smooth, add 8 oz sour cream, 1 tablespoon vanilla extract, zest from 1 orange and 2 tablespoons orange liquor and mix to combine. Mix in 8 oz semi-sweet chocolate (melted).
• Whisk together 3 large eggss and 1 large yolk and add in three stages, scraping well after each addition. Mix just until the eggs are combined, do not over mix.
• Pour the batter into the cake pan, rap the pan on the counter a few times to release air bubbles from the batter. Set the pan into a larger pan. Set the pan into the middle rack of the oven and pour water to come at least 1/2 way up the side of the cheesecake pan.
• Bake until the cake softly jiggles as a mass when the pan is shaken, it will be slightly looser in the middle, about 50 minutes. Remove from the oven and cool for 5 minutes.
• Run a thin sharp knife that has been moistened with warm water around the sides of the cake to release it from the pan (this will prevent the cake from cracking while it cools). Refrigerate several hours or overnight.

Assembly

• Run a thin, sharp knife between the cake and the pan to release the sides. If using a spring form pan release the pan. If using a regular cake pan, dip the pan briefly in hot water or run a blow torch around the sides of the pan. Flip the cake onto a plate the flip back onto a serving plate.
• Arrange orange slices in a pretty pattern on top of the cake. Warm the marmalade in the microwave, then strain to remove fruit chunks. Brush the orange slices with the marmalade.
• Refrigerate until serving. I like to remove the cheesecake from the refrigerator 1/2 hour before serving.