To a high speed blender or nutribullet combine the drained cashews, honey, vanilla extract and 2 cups almond milk and blend until completely smooth.
Pour the cashew mixture into a saucepan on medium heat. Stir in the cinnamon, nutmeg and salt. Bring to a gentle simmer for 4 minutes, whisking while it heats to ensure that it doesn't clump.
After 4 minutes the eggnog should have begun to thicken. Remove it from the heat, transfer it to a container and place it in the fridge (or freezer) until it has completely cooled.
Once the eggnog is cool transfer it to the blender along with 1/2 cup almond milk* and blend for a few seconds until its frothy. Divide between 4 glasses, add in the alcohol if using and sprinkle with cinnamon or nutmeg before serving.
Notes
* if adding alcohol, you may not need to add the 1/2 cup almond milk as the alcohol will thin out the eggnog.