In a cold saucepan, whisk together the cocoa and the sugar until all lumps are removed. Then, whisk in the salt and water, and bring to a boil over medium to medium-high heat.
Reduce to a simmer, stirring constantly, then simmer for 30 seconds to 1 minute.
Remove from heat and set aside to cool completely. Sauce will thicken as it cools.
Stir in vanilla, then pour into a glass jar, cover, and refrigerate. Makes approximately 14 ounces.
