Combine the sugar and water in a saucepan over a low heat, stir to dissolve the sugar, about 5 minutes. Increase the temperature and bring the mixture to the boil until it looks like the colour of strong tea. Remove from the heat and pour in the cream. Add the salt and vanilla then allow to cool completely.
Cream the butter in a mixing bowl and add the icing sugar. Add the caramel and mix well. Use or store until needed.