Fill a large bowl or container with ice and cold water; set aside.
Whisk the eggs, sugar, and salt in a saucepan set over low heat.
Slowly add in 2 cups milk while whisking.
Cook and stir frequently for about 20 to 25 minutes or until the temperature of the mixture registers at 160˚F. Do not bring it to a boil.
Transfer the cooked mixture to a large mixing bowl and whisk in the vanilla, bourbon, nutmeg, and remaining 2 cups of milk.
Immediately place the bowl in the previously prepared ice-water bath, whisking the milk continuously until the mixture is completely cooled.
Cover and refrigerate for at least 3 to 4 hours or until very cold.
Before serving, using an electric mixer, beat the heavy cream until soft peaks form.
Whisk the whipped cream into the eggnog until completely blended.
Pour into drinking glasses, garnish with a sprinkle of nutmeg, cinnamon sticks, holiday cookies, and serve.