1 liqueur glass Fernet Branca (1 oz)
Add to a Highball glass (*) with a lump of ice. Fizz with soda water.
(*) The beginning of the book delineates a Highball glass to be a 6 oz vessel. I ended up chilling the ingredients (without dilution), adding them to a 5 oz glass (pardon or enjoy the mismatching of amaro brands), and topping with 2 oz soda water. I added an orange twist to the recipe.