whisk egg yolks and sugar in a glass bowl until creamy.
in a saucepan over medium heat whisk the milk, cream, salt and nutmeg until it comes to a simmer.
scoop a little bit of warm milk over the egg and sugar mixture. Keep doing this until all the milk is combined with the egg/sugar (tempering the eggs like this prevents them from scrambling).
add mixture back to the saucepan over low-medium heat and mix continuously for about 3-5 minutes until it becomes a little more thick (remove from heat the second the milk starts to thicken - not a second longer or the eggs will scramble).
Remove the eggnog from heating element and add vanilla extract stirring to combine.
Make espresso using whatever method you have availavle to you (concentrate, Nesspresso, percolator).
add egg nog to your mugs and top with espresso.
Sprinkle with cinnamon on top and enjoy!
