Place coconut milk, non-dairy milk, sugar and vanilla into a tall-rimmed sauce pan (use a bigger sauce pan to avoid boiling over). Heat on medium heat to bring to a light boil, whisking frequently to dissolve and blend all ingredients together. Once at a gentle boil, reduce heat to low and leave to cook for an hour to allow the liquids to reduce (hence for the mixture to become condensed). Stir occasionally to keep ingredients combined, and keep an eye on the mixture to make sure it doesn't boil over by accident.
Once an hour has passed, it's time to thicken the mixture. In a separate cup or small bowl mix arrowroot with 2 tbsp water to create a slurry. Pour this mixture into the saucepan and using a whisk blend the mixture until it's uniform. Take it off the stove and allow it to sit for 5 minutes to thicken. At this point the mixture will look a little gelatinous (glossy and thick). Make another slurry by mixing coconut flour in 2 tbsp water. Pour this into the sauce pan and once again using a whisk combine the mixture until it's blended through. (Note: you can probably skip this step by simply allowing the mixture to cook on the stove for another 1-2 hours. I'm just not that patient ;) )
Pour into a glass jar and allow it to cool to room temperature. Store in the fridge or use immediately in a recipe.