from The Savoy Cocktail Book
Use two large silver mugs with handles. Put the whisky into one mug, and the boiling water into the other, ignite the whisky with fire, and while blazing mix both ingredients by pouring them four or five times from one mug to the other. If well done, this will have the appearance of a continued stream of liquid fire. Sweeten with one teaspoonful of powdered white sugar, and serve in a small bar tumbler, with a piece of lemon peel.