Combine the water, coconut sugar, agave, cocoa powder and espresso powder (if using) in a heavy sauce pan and bring to a boil over medium heat stirring until smooth. Boil for 5 minutes or until it starts to thicken. Whisk in the vanilla and let cool for about an hour – the sauce will thicken more as it cools.
Store in a covered container in the fridge for up to 10 days. Serve warm or cold. The sauce can be re-heated for a hot fudge sauce by microwaving for a minute or so on high power.