In a medium bowl, whisk together the egg yolks and granulated sugar until the mixture is thick and pale. This should take about 2-3 minutes.
In a saucepan over medium heat, combine the milk, heavy cream, split vanilla bean (both pod and seeds), ground nutmeg, cinnamon, and sea salt. Stir occasionally until the mixture is hot but not boiling (about 5-7 minutes).
Once the milk mixture is hot, slowly pour it into the egg yolk mixture, whisking continually to prevent the eggs from scrambling.
Pour the combined mixture back into the saucepan and cook over low heat, stirring constantly until the mixture thickens enough to coat the back of a spoon (about 5-10 minutes). Be careful not to let it boil.
Remove the saucepan from heat and stir in the vanilla extract. Discard the vanilla bean pod.
Allow the eggnog to cool to room temperature, then refrigerate for at least 2 hours, or until chilled.
To serve, give the eggnog a gentle stir, pour it into glasses, and top with a dollop of whipped cream. Sprinkle with ground nutmeg and cinnamon to garnish.
Notes
Serve in festive glasses with a cinnamon stick or vanilla bean as a stirrer for an elegant touch.