Heating milk: Heat milk, making sure it does not break the boil.
Mixing eggs and milk: Mix eggs, sugar, and salt. Whisk until it is thoroughly mixed. Add the milk, starting with small quantities and mixing thoroughly before adding more milk. Stir in coffee.
Heating eggnog: Return the eggnog to the pot and heat over medium-low heat, stirring until it starts to become foamy and a bit thicker (about 5 mins).
Cooling and serving: Remove the eggnog from the heat and whisk until it becomes a bit cooler (so it doesn't form a crust). Sprinkle with nutmeg. Serve immediately.
Video
Notes
If you want to make the chocolate version, substitute ¼ cup of unsweetened powdered cocoa dissolved in an extra cup of hot evaporated milk for the cup of coffee.For a keto version use heavy cream instead of evaporated milk, and, instead of adding sugar on the second step, sweeten to taste with sweetener of your choice once the eggs are cooked through.