In a medium bowl, add the egg yolks and sugar. Whisk together until light and creamy.
In a saucepan over medium-high heat, combine the coconut milk, cashew milk and salt. Stir often, until the mixture just begins to simmer.
Add a big spoonful of the hot milk to the egg mixture, whisking vigorously. Repeat, adding a big spoonful at a time, to temper the eggs.
Once most of the hot milk has been added to the eggs, pour the mixture back into the saucepan on the stove.
Place over medium-low heat and cook, whisking constantly, until the mixture reaches 160°F to 165°F (2 to 5 minutes).The mixture should be just slightly thickened, it will continue to thicken as it cools.
Immediately pour the custard through a fine-mesh strainer into a large bowl; stir in the vanilla, nutmeg and alcohol if using (see note).
Cover with plastic wrap and refrigerate until well chilled, at least three hours and up to one week.
The dairy-free eggnog will thicken as it cools. If you want a thinner eggnog, pour the mixture into a blender with 2-3 tablespoons of cashew milk and blend until smooth.
Serve with dairy-free whipped cream and a sprinkle of cinnamon/nutmeg. Enjoy!