1. Place the cinnamon stick in the milk.
2. Heat the milk on the stovetop in a large saucepan until just simmering.
3. Add the spices, vanilla, and molasses.
4. Carefully ladle a small amount of the hot milk mixture into the egg mixture, constantly whisking as the milk is poured over the eggs. Repeat 2-3 times.
5. Add the egg mixture into the rest of the milk mixture on the stove.
6. Bring the mixture to a simmer.
7. Place a candy thermometer in the mixture and turn off the heat when it reaches 160°F degrees.
8. Place in a large glass bowl and cover. Chill for at least four hours.
9. Mix in the rum when the mixture has chilled.