The drink was created in 1915 at the New York Bar in Paris - later Harry's New York Bar - by barman Harry MacElhone. The combination was said to have such a kick that it felt like being shelled with the powerful French 75mm field gun, also called a "75 Cocktail", or "Soixante Quinze" in French. The French 75 was popularized in America at the Stork Club in New York.
Fill a shaker with ice cubes. Add gin, lemon juice and simple syrup. Shake and strain into a chilled champagne glass. Top up with champagne. Garnish with lemon.