In a medium saucepan, bring 3 cups of fresh apple cider to a boil over medium heat. Optionally, add mulling spices like cinnamon or cloves. Allow the cider to simmer until it thickens to about 1/3 cup, which should take 20-30 minutes. Once reduced, take it off the heat and let it cool completely.

Preheat your oven to 350°F (175°C). In a food processor, grind digestive cookies or graham crackers into fine crumbs. Combine these crumbs with melted unsalted butter, a pinch of salt, and powdered sugar until crumbly. Press this mixture evenly into the bottom of a greased 9" springform pan, then bake for 10 minutes. Let it cool.

In a stand mixer, beat softened cream cheese and brown sugar on medium speed until smooth and creamy. Add in the cooled reduced apple cider, sour cream, vanilla extract, and a sprinkle of cinnamon. Continue mixing until fully combined and no lumps remain.

Add the room temperature eggs to the mixture one at a time, mixing on low just until incorporated after each addition. Sift in the all-purpose flour, continuing to blend on low speed only until the flour is fully combined.

Pour the cheesecake filling into the cooled crust, smoothing it gently with a spatula. To create a water bath, place the springform pan inside a larger pan filled with hot water, ensuring the water reaches halfway up the sides of the springform pan. Bake at 325°F (163°C) for 80-90 minutes.

After baking, turn off the oven while leaving the cheesecake inside. Crack the oven door with a wooden spoon to allow gradual cooling, and let it rest for about 30 minutes. Once cooled, transfer the cheesecake to the countertop to cool completely before refrigerating.