In a medium-sized saucepan, combine the whole milk, heavy cream, granulated sugar, split vanilla bean, and the scraped vanilla seeds. Place the saucepan over medium heat, stirring occasionally until the sugar has fully dissolved, and the mixture is warmed through, but do not allow it to reach a boil.
While the milk mixture is heating, crack the eggs into a separate mixing bowl and whisk them until the yolks and whites are fully blended. To temper the eggs and prevent curdling, gradually pour about 1 cup of the warm milk mixture into the eggs, whisking vigorously as you do so.
Once the eggs are tempered, slowly pour the egg mixture back into the saucepan with the remaining milk mixture. Continue to whisk constantly to combine and ensure a smooth consistency.
Cook the combined mixture over medium-low heat, stirring continuously until it thickens slightly and reaches a gentle simmer, or a temperature of about 160°F (70°C). Avoid boiling the mixture, as this could cause it to curdle.
After reaching the desired temperature, remove the saucepan from the heat. Stir in the ground nutmeg, ground cinnamon, and pure vanilla extract until fully incorporated.
Allow the eggnog to cool to room temperature before transferring it to the refrigerator. Chill for at least 2 hours to enhance the flavors and achieve a cold, refreshing drink.
To serve, pour the chilled eggnog into festive glasses, topping each serving with a generous dollop of whipped cream and a light dusting of grated nutmeg.
Notes
For a delightful presentation, use elegant glassware and garnish with a cinnamon stick or a light sprinkle of cocoa powder on top for a seasonal touch!