The Vesper features in Ian Fleming’s novel, Casino Royale, agent 007 instructs a bartender to mix “three measures Gordon’s, one of vodka, a half measure of Kina Lillet.
Below you'll find an adapted version as I think almost 5oz is a pretty hefty drink!
Kina Lillet is a quinquina, a type of bitter aperitif made with cinchona bark. It was a key component in the original recipe but was discontinued in the late 1960s.
The best substitute for the Kina Lillet is Cocchi Americano, an Italian aperitif made with a base of Moscato wine macerated with herbs, spices, gentian root and cinchona bark. It has a herbal complexity with a soft sweetness and a bitter bite. Using Cocchi Americano in a Vesper creates a cocktail that is dry, bright and citrusy, with a very subtle bitter note.
If you don’t have Cocchi but do have a bottle of Lillet Blanc then simply add a few dashes of Angostura Bitters - it won’t look like the most pristine Vesper but it will improve it’s flavour profile compared to that of Lillet on it’s own.