Preheat oven to 375ºF.

Wrap the outside of a 9"/23cm spring-form pan with aluminum foil. (This will seal the pan so no water gets in, as the cake is baked in a water bath.)

In a bowl, combine the gingersnap crumbs, sugar, and melted butter.

Press the crust into the pan, letting it come about ¼-½ inch up the sides.

Bake the crust until lightly golden, 5-6 minutes. Cool completely.

In a food processor (or by hand), process the cream cheese, sour cream, pumpkin and sugars until smooth.

Add the eggs and extra yolk one at a time, processing briefly between each addition.

Add the vanilla, cinnamon, ginger, chai, nutmeg and salt. Process to combine.

Strain the custard through a fine mesh sieve into the cooled crust.

Transfer the pan to a large casserole and fill the dish with warm water so that it reaches a quarter of the way up the cake pan.

Bake until the custard is set around the edge but still slightly loose in the center when jiggled, approximately 45 mins to 1 hour.

Cool the cake at room temperature for 1 hour, then chill until set.