In a cold saucepan, whisk together the cocoa and the sugar until all lumps are removed. Add the salt and the water and bring to a boil over medium-medium high heat.
Reduce to a gentle simmer; stirring constantly. Simmer for about 30 seconds and then remove from heat. Let cool and then add in the vanilla.
Pour into a glass jar and allow to cool. {The chocolate sauce will be very thin when it finishes boiling, but it will thicken quite a bit as it cools.}