In a heavy saucepan (at least 5 cup capacity), stir together the sugar, syrup, and water until the sugar is completely moistened. Place your candy thermometer into the pot taking care that it is tip in immersed into the sugar mixture.Heat, stirring constantly, until the sugar dissolves and the syrup is bubbling.Stop stirring completely and allow it to boil undisturbed until it turns a deep amber (like the color of Bass Ale) (see notes below).Immediately remove it from the heat and slowly and carefully pour the hot cream into the caramel. It will bubble up furiously.Use a high-temperature heat-resistant rubber spatula or wooden spoon to stir the mixture until smooth, scraping up the thicker part that settles on the bottom. If any lumps develop, return the pan to the heat and stir until they dissolve.Stir in the butter and salt. The mixture will be streaky but become uniform after cooling slightly and stirring.Allow the sauce to cool for 3 minutes. Gently stir in the vanilla extract.