In a 3 quart saucepan, heat the water and sugar over medium heat. Make sure you use this larger size saucepan as the mixture will bubble vigorously when you add the butter and cream. Stir constantly until the sugar has dissolved and the mixture bubbles slightly. 

Increase the heat to high and bring to a boil.  Do not stir any more.  Let the mixture boil until it becomes an amber color (350 degrees if using an instant read or candy thermometer). 

Add in butter and whisk constantly until it is completely melted.

Remove from heat and very slowly whisk in cream.  The mixture will bubble vigorously, so be very careful as you whisk.  Once the cream is incorporated whisk in the vanilla and the salt.  

Pour into dish or jar and allow to cool completely before you use or store.  It will thicken as it cools.  Will keep in the refrigerator for a month.