01 - Combine almond milk and heavy cream in a medium saucepan over medium heat. Warm gently until steaming, but do not allow the mixture to come to a boil.
02 - Whisk eggs and powdered erythritol in a mixing bowl until the mixture becomes pale in color and smooth in texture.
03 - Gradually ladle small amounts of the warm milk mixture into the eggs while whisking continuously. This prevents the eggs from scrambling when added to the hot liquid.
04 - Pour the tempered egg mixture back into the saucepan. Cook over low heat, stirring constantly with a whisk or wooden spoon, until the mixture thickens enough to coat the back of a spoon, approximately 5–8 minutes.
05 - Remove from heat immediately. Stir in ground nutmeg, ground cinnamon, and vanilla extract until fully incorporated. Add rum or bourbon at this stage if using.
06 - Transfer the eggnog to a bowl or pitcher. Refrigerate for at least 1 hour, or until completely chilled.
07 - Pour cold eggnog into serving glasses. Top with whipped cream and dust with additional nutmeg or cinnamon before serving.