In a small pot over high heat, add the apple cider, sugar, vanilla, apple slices, and cinnamon.
Bring to a boil and then reduce the heat to a simmer.
Simmer for 15 minutes then turn off the heat.
Strain the syrup (save the strained apples to enjoy in another dish!), then allow it to cool before storing it in an airtight container in the refrigerator for up to 2 weeks.