1. Combine flour, powdered sugar, and salt. Cut in cold butter until the mixture resembles coarse crumbs. Mix in egg yolk and cold water just until dough comes together. Form into a disk, wrap, and chill for 30 minutes.

2. Roll out dough and press into tart pan. Chill again, then blind bake at 375°F for 15 minutes. Remove weights and bake another 10 minutes until golden.

3. Whisk egg yolks with sugar, cornstarch, and nutmeg. Heat eggnog until simmering, then slowly whisk into yolk mixture. Return to pan and cook until thick. Remove from heat, stir in butter and vanilla.

4. Pour warm pastry cream into cooled crust. Smooth top, cover with plastic wrap touching the surface, and chill at least 4 hours.

5. Melt ½ cup sugar over medium heat until amber. Pour onto parchment paper and let cool. Once hardened, break into shards.

6. Top tart with caramel shards just before serving.