01 - Combine almond milk and heavy cream in a medium saucepan over medium heat. Warm gently until steaming, but do not boil.
02 - Whisk eggs and powdered erythritol in a mixing bowl until pale and smooth.
03 - Gradually ladle the warm milk mixture into the eggs while whisking constantly. This tempers the eggs and prevents curdling.
04 - Return the mixture to the saucepan. Cook over low heat, stirring constantly, until the mixture thickens slightly and coats the back of a spoon, about 5 to 8 minutes.
05 - Remove from heat. Stir in ground nutmeg, ground cinnamon, and vanilla extract. Add rum or bourbon now if using.
06 - Pour into a bowl or pitcher. Refrigerate for at least 1 hour until completely chilled.
07 - Pour cold eggnog into glasses. Top with whipped cream and dust with additional nutmeg or cinnamon.