Pour the oat milk into a saucepan. Add the molasses, honey, cinnamon powder, salt, and any optional spices.
Place the saucepan on the stove over medium-high heat. Stir frequently until the mixture reaches a boil (when it starts to bubble vigorously). Continue stirring until the molasses and honey are completely dissolved.
Remove the saucepan from the heat, cover it with a lid, and let it stand for 5 minutes.
If you used whole spices (like cloves, allspice grains, or star anise), strain the mixture through a fine sieve into serving cups. If you used only ground cinnamon, pour directly into cups.
Serve immediately. Any leftover serving can be covered, refrigerated, and reheated the next day.