Mix the sugar, cocoa, and salt in a saucepan. Add the water and mix well. Bring to a boil stirring constantly, then reduce the heat and simmer for 2 or 3 minutes. Be careful not to burn. Chocolate scorches easily so don’t leave this unattended. Remove from heat and add vanilla extract if using it. Once the syrup is cool, store in the refrigerator. This can be used to make chocolate milk, milkshakes, or poured over ice cream. A single batch makes about 1 cup. Syrup can be made thicker by reducing the amount of water used.