Mix egg yolks, 2 cups of coconut/almond milk or cream, and sugar. Stir gently but constantly over medium-low heat until the mixture thickens enough to cling to and coat the back of a spoon, about five to ten minutes. Be patient with this process – if you turn the heat up too high or don’t stir, the egg yolks might turn into scramble eggs.
Remove from heat and set the pot in a larger bowl filled with ice water (careful, so no water overflows into the eggnog!) and stir for 2-3 minutes then add the last cup of milk/cream and the vanilla.
If you want to add any additional holiday spirit (a few tablespoons of rum, bourbon or whiskey) to the eggnog, now is your chance. Let the mixture cool down to room temperature then chill for a while longer in the fridge. The longer you let the eggnog chill, the thicker and more custard-like it will become. Before serving, generously dust with cinnamon and nutmeg. If you can, buy whole nutmeg and grate it yourself (a microplane zester works great for this).