Mix the cocoa, sugar and water in a sauce pan on the stove at a medium high heat, whisking constantly.
Heat until boiling and then boil for 1 minute more. Still, whisking constantly.
Remove from heat and slightly cool.
At this point you can add a pinch of sea salt, if you'd like
Next, add vanilla extract and cool completely
Store in a covered glass jar in the fridge.
Syrup will thicken as it cools.