This is a classic and early 20th century gem. The Aviation cocktail was first published in Hugo Ensslin’s 1916 “Recipes for Mixed Drinks.” In that original iteration, it used two dashes of crème de violette. When Harry Craddock included the cocktail in his “Savoy Cocktail Book” in 1930, the violette was omitted. This may be because that the violette wasn’t readily available at the time. Still elusive in some parts of the world, violette remains optional. If you do get your hands on it, dash it sparingly; it’s delicious but tends to dominate.