In a large heavy saucepan, put the sugar and water and stir. Have all of the other ingredients at the ready.
Over medium high heat, bring to a boil. Do not stir. Swirl the pan often. It should boil for around 15 minutes or until it turns a medium amber color. Use a pastry brush dipped in water to move any sugar crystals on the sides of the pan into the boiling mixture.
As soon as the color looks good, remove the pan from the heat and pour in the cream. Be careful as it will bubble like crazy!
Whisk the cream in, then the butter, vanilla and salt. Whisk until smooth and leave to cool. Once cool, pour into 2 one cup (8 oz) jars and refrigerate.
Notes
The longer you boil the sugar, the deeper the colour of the sauce. Use a deep pot for this recipe, because of the bubbling action when pouring in the cream.The sauce will thicken as it cools. Jars will keep in the fridge for up to a month.