Add the milk and spices to a small pot and simmer gently for 15 minutes. Turn off the heat and let the spices steep for another 15-20 minutes.
Strain out the spices. Add 3 egg yolks to the milk. Use an immersion blender to blend until frothy. Heat gently, stirring often, for about 10 minutes.
Remove from the heat. Let cool for 5 minutes or so and serve hot, with rum, if desired; or cool to room temperature, add the rum and then refrigerate for an hour or more before serving. Store in the refrigerator and consume within a few days.