Combine the water or milk, hemp hearts (if using), sweet potato, 3 tablespoons of maple syrup, vanilla, nutmeg, cinnamon, ginger, and salt in a blender. Blend until smooth.
Taste the drink and add another tablespoon of maple syrup if you'd like it to be sweeter. (Keep in mind that sweetness is muted when chilled, so it won't taste quite as sweet when you serve it cold.)
You can serve the eggnog right away, if you'd like to, but I like to chill it for 1 to 2 hours before serving. Add alcohol if you like. Leftover eggnog can be stored in an airtight container in the fridge for up to 4 days. (It makes a great coffee creamer!)