Add all the ingredients except Xanthan Gum to a saucepan, whisk and then heat over medium. Bring to a light boil.
Reduce heat to medium low, simmer for about 15 minutes or until reduced by about half. You should have about 3/4 cup / 7 oz / 200 ml.If using Xanthan Gum to thicken, whisk vigorously while sprinkling in just a dash or two of the Xanthan Gum. Make sure you don't add too much or the sauce will get goopy.
Let cool for 10 minutes, then strain (with a fine mesh strainer) into a jar or bottle. Use right away or store in the fridge for up to 1 month.
Notes
*I did try a version using some Tamarind and found that it was good, but there wasn't enough of a difference to warrant including it as a necessary ingredient.Especially since it's less common than the other ingredients. But if you want to include it, I would add 1 - 2 Tbsp.