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.
Notes
Don't stop stirring/whisking. Doing so will result in thick films which will need to be discarded.
Temper the eggs. If you don't temper the eggs properly, they'll either cook in the pot or begin to separate once the eggnog is done.
Use a non-stick saucepan. Avoid stainless steel pots. Use a nonstick pot for a no-mess eggnog.
Use a silicone spatula. Silicone spatulas are best for cleaning out pots and bowls. You can scrape the bottom and sides of the pot clean to avoid bits of burnt eggnog stuck in the pot.