In a medium saucepan, combine the sugar and water and bring to a boil, whisking until the sugar melts. Turn to medium heat and slowly boil without whisking until until a deep amber caramel forms, about 6 minutes. Remove the saucepan from the heat and carefully whisk in the butter; it will foam up. Whisk in the cream (it will foam up again) and salt.

Let the caramel cool to room temperature and store in a glass container for up to 2 weeks in the fridge.