Begin by pouring 3 cups of fresh apple cider into a saucepan. Bring it to a rolling boil over medium-high heat, adding mulling spices if desired. Allow it to simmer for 30 to 45 minutes until it thickens and reduces to about ⅓ cup. Remove from heat and let it cool to room temperature.

While the cider cools, preheat your oven to 350°F (175°C) and line the bottom of a 9-inch springform pan with parchment paper.

In a food processor, crush the digestive cookies or graham crackers into fine crumbs. Combine the crumbs with melted unsalted butter and brown sugar in a bowl, and press the mixture into the bottom of the prepared springform pan. Bake for 10 minutes until set, then let it cool completely.

In a mixing bowl, beat the room-temperature cream cheese and brown sugar until smooth. Blend in the cooled apple cider, sour cream, vanilla extract, and a pinch of cinnamon until combined.

Add the eggs one at a time, mixing gently after each addition. Fold in the all-purpose flour until just combined.

Pour the cheesecake filling into the cooled crust and smooth the top. Place the springform pan into a larger baking dish filled halfway with hot water and bake for 80 to 90 minutes.

After baking, turn off the oven and crack the door open slightly. Allow the cheesecake to cool in the oven for about 30 minutes. Transfer the pan to the counter to cool completely, then refrigerate for at least 8 hours or overnight.