In a bowl or medium sized pot, add egg yolks and beat with whisk or hand mixer.
Stir in sugar, mix well to combine.
In another pan, add milk.
Then add cream.
Stir in spices and vanilla.
Heat cream and milk, while whisking vigorously, over medium high heat to hot - but NOT boiling.
Slowly temper eggs by pouring milk and cream mixture into eggs while whisking vigorously. Pour only a little bit of the cream and milk at a time, so you do not cook the eggs and make scrambled eggs!
Whisk well when fully mixed.
Return pot to stove and cook on medium heat, whisking vigorously, until eggnog thickens (about 4-5 minutes) - and reaches 160 degrees Fahrenheit using a candy thermometer.
Remove from heat and strain.
Let cool in refrigerator for at least 30 minutes.
Serve with a cinnamon stick and a bit of fresh nutmeg grated on top.
Stir in a shot of rum or whiskey as desired.
Can also be heated up to serve hot, if desired.