Whisk together the egg yolks and the sugar until light and creamy.
Then in a saucepan over medium heat, combine the heavy cream, milk and cinnamon. Stir and heat until the mixture reaches a simmer.
Next gradually add the hot milk to the egg mixture (1 spoonful at a time) whisking after the addition of each spoonful. You want to gradually add in the heated milk so that you do not scramble the eggs. Follow this process until all the milk has been added to the egg mixture.
Then pour the mixture back into the saucepan on the stove.
Heat on medium low heat and whisk until the mixture is slightly thickened. It will thicken more as it cools.
Remove from the heat and then stir in the vanilla extract.
Store in the mixture in the refrigerator until chilled and thickened.
Serve topped with fresh whipped cream and additional cinnamon if you prefer.
Enjoy!
Notes
Store the egg nog in an air tight container in the refrigerator for up to 1 week.