Place all of the ingredients except the xanthan gum together in a mixing bowl. Whisk to combine.

Pour the mixture into a saucepan and heat over medium heat. Bring to a light boil for 10 minutes.

Reduce the heat and whisk in the xanthan gum until the mixture thickens.

Remove from the heat and allow to cool. Don’t worry - the mixture will thicken more as it cools.

Serve immediately or store in an airtight container in the fridge.