In a medium saucepan, add the cocoa powder and granulated sugar. Whisk them together until they are evenly mixed.
Slowly pour in the cold water while continuing to whisk the mixture.
Place the saucepan over medium heat. Keep whisking as the mixture heats up, bringing it to a gentle boil.
Once the syrup reaches a boil, reduce the heat to low. Stir in the kosher salt and vanilla extract, mixing well.
Let the mixture simmer for about 5-10 minutes, stirring occasionally, until it thickens. Add more water if too thick.
Remove from heat and allow to cool. Transfer to a storage container and refrigerate.
