Meanwhile, to make the toffee sauce, melt the butter in a large saucepan over a medium-low heat, then add the brown sugar. Let this come to the boil, then cook for 2 to 3 minutes, until the sugar has an intense caramel colour and flavour, but be careful not to burn the caramel! Pour in the cream and whisk continuously. The mixture will clog a little, but don’t panic. Let it come to a boil again, then reduce to a gentle simmer. Cook for 2 to 4 minutes, until it coats the back of a spoon.