Add the water and sugar to a saucepan, place over medium heat, and melt the sugar until golden or amber - about 7-10 minutes.

Meanwhile, heat the cream very well and have the butter and salt ready.

As soon as the caramel reaches the right color, remove the saucepan from the heat, add the butter, and stir quickly with a spatula.

Quickly pour in the hot cream, stirring constantly. The mixture will hiss and bubble vigorously - that's normal.

Return the saucepan to medium heat and cook for another 5 minutes, adding salt if you like.

Pour the toffee into a glass container, let cool at room temperature, and store in the fridge.