In a small mixing bowl, store the egg yolks, separating them from the whites. Set aside.
In a medium sauce pan, add the sugar, cream, milk, nutmeg, vanilla extract and cinnamon stick.
Whisk over low/medium heat until very warm and the sugar has fully dissolved.
Slowly add 1/2 cup of the warm milk to the egg yolks at a time, stirring between each addition. The goal is to slowly warm the egg yolks because if they go from cold to hot too quickly they can curdle.
Once the mixing bowl with the milk and yolks feels very warm to the touch (on the outside of the bowl), whisk the mixture back into the pan.
Heat until the liquid reaches 160°F (71°C).
Strain to remove any sediments and the cinnamon stick. Store in the refrigerator.