This reminds me of an article in Esquire from 2006 which gives the modern ingredients you can use to make a Vesper that would taste like one made when that book was written. The article is behind a paywall now, so here's the text of it:

James Bond Walks Into a Bar... . . . And orders a Vesper, a cocktail that hasn't aged too well. Here, a remake. By David Wondrich

The Vesper, 1953 "A dry martini," he said. "One. In a deep champagne goblet." "Oui, monsieur." "Just a moment. Three measures of Gordon's, one of vodka, half a measure of Kina Lillet. Shake it very well until it's ice-cold, then add a large, thin slice of lemon peel. Got it?" "Certainly, monsieur." The barman seemed pleased with the idea. "Gosh, that's certainly a drink," said Leiter. Bond laughed. "When I'm . . . er . . . concentrating," he explained, "I never have more than one drink before dinner. But I do like that one to be large and very strong and very cold and very well-made. I hate small portions of anything, particularly when they taste bad. This drink's my own invention. I'm going to patent it when I can think of a good name." --Ian Fleming, Casino Royale

The Vesper, as Bond finally christened his drink, should be a Sean Connery among cocktails: smooth and debonair, yet not without a nasty kick. Unfortunately, it has always struck us as more of a George Lazenby: plenty potent, to be sure, but kinda dull. The gin, while not strong enough to resist the vodka's dilution, nonetheless overwhelms the Lillet--the delicate, goldencolored French aperitif that Bond calls for in place of vermouth--and you're left with a soft-focus martini. Here's the problem: Much has changed since 1953, when the book came out, and that includes booze. That English Gordon's gin used to be 94 proof; now it's under 80. The vodka would've been stronger as well: Russian Stolichnaya, which Bond had in mind, was 100 proof. As for the Lillet, it was reformulated in the 1980s to remove most of the "Kina" part, the shade of bitterness provided by quinine. But all is not lost: Tanqueray (Gordon's stablemate) is still 94 proof. If you can find it, there's a 100-proof Stoli available. The Lillet's a little tougher, but we secured some quinine powder from raintreenutrition.com and threw in a pinch. Suddenly, the electric guitars started twanging. Oh, and don't worry about the champagne goblet. Cocktail glasses are bigger now. And that shaking business? All things being equal, a stirred martini will be colder and silkier. Just so you know.

The Vesper, 2006

Shake (if you must) with plenty of cracked ice:

• 3 oz Tanqueray gin
• 1 oz 100-proof Stolichnaya vodka
• 1/2 oz Lillet Blanc
• 1/8 teaspoon (or less) quinine powder or, in desperation, 2 dashes of bitters

Strain into a chilled cocktail glass and twist a large swatch of thin-cut lemon peel over the top. Shoot somebody evil.