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 to medium high heat.
Reduce to a simmer; stirring constantly. Simmer for about 30 seconds and then remove from heat. Let cool and then add vanilla. Pour into a glass jar and refrigerate until needed.
Note:The chocolate sauce will be very thin when it finishes boiling, but it will thicken quite a bit as it cools. The chocolate sauce may be stored in the refrigerator for up to two weeks. Simply reheat before serving.