Put the sugar in a large pan and let it melt at medium heat while stirring constantly until the caramel is dark gold and no lumps are visible.
Remove the pan from the heat, carefully add the cream and stir. Heat the pan again slightly and stir over a low heat until the caramel is liquid. Add butter and whiskey, stir well and pour into a bottle.
Close well, let it cool down and put it in a cool place. Use up quickly.