Cut the vanilla pod into halves, and use a knife or spoon to scrape out the seeds. Mix the vanilla seeds with the sugar in a small mixing bowl.
Pour the vanilla sugar, port wine, orange juice, cherry wine, and water into a pot and set it on the stove. Bring to a boil while stirring gently, then turn the sauce down to a gentle simmer and let it cook for a few minutes.
Next, gently transfer the cherries to the pot and mix to combine. Bring to a boil again, before turning the sauce down to a simmer. Let it simmer for 10-minutes.
Now, in a small mixing bowl, whisk the cornstarch together with a few tablespoons of cold water.
Whisk teaspoons of cornstarch into the sauce a little at a time until the sauce has the thickness you prefer.
Remove from the heat and set aside. The sauce can be stored in the refrigerator until you’re ready to serve.