Combine evaporated milk, sweetened condensed milk, and cinnamon stick in a pot over low to medium heat.
In a bowl, whisk egg yolks until slightly thickened, about 2 minutes. Slowly pour in coffee while stirring continuously.
Add the coffee mixture to the pot, bring to a boil, and simmer on low for 5 minutes until slightly thickened. Add sugar to taste, a sprinkle nutmeg on top, and serve. Buen provecho!