Preheat your oven to 325°F (163°C) and prepare a 9-inch springform pan by lining it with parchment paper and greasing the sides with butter.

In a mixing bowl, combine shortbread crumbs, sugar, cinnamon, and melted butter. Press into the bottom of the pan and bake for 10 minutes. Cool completely.

Lower the oven temperature to 300°F (148°C). In a bowl, beat cream cheese, brown sugar, and flour until smooth. Mix in sour cream, molasses, vanilla, and spices.

Add eggs one at a time, mixing gently. Pour the filling into the cooled crust.

Wrap the pan with foil and place in a larger dish filled with warm water halfway up the sides. Bake for 1 hour and 20 minutes.

Turn off the oven and let the cheesecake cool inside for 1 hour with the door ajar.

Cool at room temperature for 30 minutes, then refrigerate for at least 5 to 6 hours, preferably overnight.

Whip heavy cream, powdered sugar, molasses, and spices until soft peaks form. Fold in cream cheese for the mousse.

Spread the mousse over the chilled cheesecake and refrigerate for 1 to 2 hours.

Optionally, decorate with whipped frosting and crushed gingerbread cookies before serving.