Put the soft brown sugar in a pan with the liquid glucose and
Remove the pan from the heat and gradually add the double cream. Start with a spoonful at a time as the mixture will rise dangerously when the cold cream hits the volcanic caramel.
When all the cream has been incorporated, gradually stir in the butter dice, until you have a smooth, creamy sauce.
You can use the sauce at once or allow to cool, then refrigerate for up to 2 weeks. Reheat gently, only returning to the boil after the butterscotch is hot.