Fill a cocktail shaker with ice cubes.
Add the gin, vodka, and Lillet Blanc.
Shake hard until well chilled.
Double-strain into a chilled cocktail glass.
Garnish with a lemon zest, expressing the oils over the surface before placing on the rim.
Purists debate shaking versus stirring - Bond famously orders it shaken, which adds aeration and dilution that slightly softens the strength. The original recipe in Ian Fleming's Casino Royale called for Kina Lillet, a now-discontinued quinine-forward aperitif wine; Lillet Blanc is the closest modern substitute, though Cocchi Americano is often preferred for its more bitter, complex character.
My Bar Shelf reads your shelf and shows you every cocktail you can make from what you already own, including Vesper.