Thick, chewy cinnamon- and cardamom-spiced snickerdoodles are fashioned as a version of thumbprint cookies here - with an indentation for a dollop of rich, smooth eggnog custard that flows over the cookie as it bakes. These two-in-one cookies channel holiday spices, and meld custard and snickerdoodle into its own dessert. Kirsten Mossberg's recipe for the cookie dough includes cream cheese for a delicate-but-sturdy texture and an added dimension of flavor.