A French 75 is a Champagne cocktail: 30ml gin, 15ml fresh lemon juice and 15ml sugar syrup, shaken hard over ice, strained into a flute and topped with chilled Champagne. Finish with a lemon twist. It is bright, dry and dangerously easy to drink. Named, so the story goes, after a field gun.

The name is the fun part. The 75 refers to the French 75mm field gun, the quick-firing artillery piece the French army leaned on in the First World War. The drink, so the legend runs, landed with the same sudden force. It turns up in print in Harry Craddock's 1930 Savoy Cocktail Book, by which point it had already been doing quiet damage at Harry's New York Bar in Paris. A century on, it remains the most charming way to open an evening.

Here is the thing about the French 75: almost nobody makes it exactly the same way twice, and almost nobody needs to feel bad about that. The bones are fixed. The details are yours.

What goes into a French 75?

The classic build is gin, lemon, sugar and Champagne, assembled in that order. Thirty millilitres of gin, fifteen of fresh lemon juice, fifteen of sugar syrup. Shake those three over ice until the tin is painfully cold, then strain into a chilled flute and top with roughly seventy-five millilitres of Champagne. A twist of lemon, expressed over the surface so its oils catch in the bubbles, and you are done. The Champagne goes in last and undisturbed; it is never shaken.

If you like a drier drink, pull the sugar back to a teaspoon. If your lemons are fierce, nudge it up. The target is a cocktail that tastes of citrus and bubbles with the gin humming underneath: not a lemonade, not a sherbet. Balance first, everything else second.

Gin or cognac?

This is the argument that refuses to die. The earliest recipes are built on gin, and gin is what most bars pour: it keeps the drink bright, crisp and upright, all lemon and juniper against the fizz. A good London Dry is the safe and brilliant choice. Sipsmith London Dry does the job beautifully: clean, classic, the kind of gin that gets out of the Champagne's way.

The other camp swears the French in French 75 should mean French brandy, and pours cognac instead. They have a point in winter. Swap the gin for a measure of Hennessy VS or Rémy Martin VSOP and the whole thing deepens: warmer, rounder, a touch more fireside. Add bourbon instead and you have wandered into a drink called the French 95, but let the purists have that fight. Both versions are correct. Pour gin for a party, cognac for a nightcap.

Which Champagne should you use?

Here is the liberating truth: you do not pour your best Champagne into a French 75. The lemon and sugar would trample a delicate vintage, and you would be mixing away the very things you paid for. What you want is a proper, dry, non-vintage brut with enough backbone to stand up to citrus. Veuve Clicquot Yellow Label, £49.99, is the textbook choice: a grande marque with the structure to hold its shape in a cocktail, and the name to make the gesture feel generous.

If you would rather save the special bottle for drinking neat, Louis Roederer Collection 246 at £45.99 is a serious house Champagne that mixes without complaint. The rule is simple: dry, cold, and nothing you would mourn. Prosecco will stand in at a pinch, and the drink becomes, strictly, a different animal; we will keep that between us.

Those two are all you need to build a proper French 75 at home: the gin for the backbone, the Champagne for the lift. Everything after that is garnish and glassware.

Flute or coupe?

Tradition says flute, and the flute has logic on its side: it keeps the bubbles marching for longer, which matters in a drink built on them. The coupe is prettier and more theatrical, and gives up its fizz a shade faster. Either is right. What matters more is that the glass is properly chilled and the Champagne properly cold. Warm fizz in a warm glass is the only real way to ruin this drink. If you want to fall down the glassware rabbit hole, we have been there.

The French 75 is an opening drink. It is what you hand people as they arrive, before the coats are off, when the night still feels full of promise. That makes it the natural companion to the party season, from the first Christmas gathering to the countdown on New Year's Eve.

It was named after a weapon, which is worth remembering around the third one. The French 75 arrives looking like innocent fizz and lands with rather more intent. Make it cold, make it dry, and make the first round before anyone has decided how the night is going to go. The gun, after all, was prized for its speed.