Prepare the tart crust by mixing flour, powdered sugar, and butter.
Add the egg yolk and cold water, mix until combined, then chill.
Roll out the dough and fit it into a tart pan.
Blind bake the tart crust until lightly golden.
Prepare the filling by whisking together eggnog, cream, vanilla, spices, and cornstarch.
Pour the filling into the baked tart shell and bake until set.
While the tart cools, prepare the caramel shards.
Cool the caramel until it hardens, then break it into shards.
Once the tart has cooled, top it with caramel shards just before serving.