In a small saucepan, whisk together the sugar and cocoa. Add a small amount of the boiling water and whisk until all of the mixture is moistened. Then whisk in the remaining boiling water. Bring the mixture to a full rolling boil on low heat. Remove the pan from the heat and allow the mixture to cool slightly. Whisk in the vanilla and Chambord, if using. Cover it tightly to prevent evaporation.