In a medium saucepan, combine your almond milk, cream, cinnamon, and nutmeg. Bring the mixture to a gentle boil. Remove from heat immediately once it starts to boil. Stir in your vanilla extract.
Pour the mixture back into the saucepan. Heat over medium-low heat, whisking constantly, until the mixture thickens slightly or reaches 160 degrees F. Do not let it boil.
If you want to add rum, add it now. Pour your eggnog into a bowl or bottle. Cover and refrigerate for 3-4 hours, until cold, or longer until ready to serve.