There comes an evening, somewhere in late September, when the spritz quietly loses the argument. The light goes amber earlier, the jumper reappears, and the drink you actually want has weight to it: something brown-spirited, tart and just sweet enough to feel like a treat. The whisky sour has been that drink for the best part of two centuries, and it asks for almost nothing you do not already own.

A sour is the simplest idea in the whole cocktail canon: a spirit, something citrus, something sweet, shaken hard and served cold. Where the Manhattan is stirred, spirit-forward and serious, the sour is its brighter, louder cousin: shaken until it is frothy, sharp on the first sip and soft on the finish. It is the drink that converts people who think they do not like whisky, because the lemon does the introductions and the bourbon simply turns up looking handsome.

None of this is new. Sours were already a fixture of American bar manuals by the 1860s, back when a bartender's reputation rested on how well he could balance spirit against citrus. The template proved so durable that half the drinks you love are sours wearing different coats: the Margarita, the Daiquiri, the Sidecar, the Gimlet. Learn the whisky version and you have, more or less, learned all of them.

The bourbon question

A sour wants a whisky with a bit of sweetness and body to stand up to the lemon, which is why bourbon is the natural home. Buffalo Trace is the everyday choice and a very good one: caramel-rich, gently spiced and reliable to the last drop, it slots into a sour without a hint of drama. Want a little more oak and swagger in the glass? Elijah Craig Small Batch carries more weight and a deeper char, and it makes a sour that tastes like it means it. And if you like things rounder still, W.L. Weller swaps the rye in its mash for wheat, softening every edge. Purists will tell you a proper rye makes the sharpest sour of all, its pepper cutting clean through the sugar, and they are not wrong. But for a first sour, reach for bourbon and let it charm you.

Lemon, sugar, and getting the balance right

Two rules, and the drink is yours. Use fresh lemon juice, squeezed that day: the bottled stuff tastes of cordial and regret, and no whisky can rescue it. And sweeten with a simple syrup rather than granulated sugar, because sugar will not dissolve properly in a cold shake and you will end up with a gritty finish. A syrup is nothing more than equal parts sugar and boiling water, stirred until clear and cooled; a jar of it lives happily in the fridge for a fortnight. Get those two right and the balance almost takes care of itself.

The egg-white question

Here is the great sour debate, and the honest answer is that both camps are right. A whisky sour is entirely delicious without egg white: tart, clean and bracing. Add a fresh egg white, though, and something rather lovely happens. It brings no real flavour of its own, but it transforms the texture, giving the drink a thick, glossy foam and a silk-pillow softness that turns a good sour into a memorable one. The trick is the dry shake: shake everything hard once without ice to whip the white into a foam, then add ice and shake again to chill and dilute. If eggs are not your thing, a splash of aquafaba, the brine from a tin of chickpeas, does almost exactly the same job and no one will ever guess.

Which brings us to the only real decision: which bottle to reach for. Start with an easy, caramel-led bourbon and trade up as your sours get more confident. These two are a sensible place to begin and to graduate to.

The build

Into a shaker, pour fifty millilitres of bourbon, twenty-five of fresh lemon juice and twenty of simple syrup. If you are going the silky route, add one fresh egg white now. Shake hard without ice for ten seconds to build the foam, then fill the shaker with ice and shake again until the outside is frosted and your arm has started to complain, around fifteen seconds. Strain into a chilled rocks glass over a large cube, or into a coupe if you are feeling elegant. Taste, and adjust to your palate: a touch more syrup if the lemon bites too hard, a squeeze more lemon if it leans sweet. Your sour, your rules.

For the garnish, a lemon twist and a good dark cocktail cherry are traditional and handsome. If you have used egg white, three drops of aromatic bitters dotted across the foam and dragged through with a cocktail stick make a small work of art, and a genuinely lovely aromatic first sip. It takes two seconds and looks like you know exactly what you are doing.

Three variations worth knowing

The New York Sour is the showpiece: make a standard sour, then float a spoonful of red wine gently over the top so it bleeds down through the foam in a slow crimson ribbon. The Gold Rush drops the sugar syrup for honey syrup, giving a richer, rounder, faintly floral drink that is very hard to stop making. And if you swap lemon for lime and bourbon for tequila you have wandered off into Margarita country, which only proves the point about sours being one big family. For a stirred, spirit-forward night instead, the Boulevardier is waiting: same whisky-season mood, none of the shaking.

The whole thing costs you one bottle, a couple of lemons and less than a minute of effort, and it improves every time you make it. The spritz had its summer. The evenings have other ideas now. Shake one properly, taste that first cold, foamy, lemon-bright sip, and you will understand why the sour never really goes out of fashion. It just waits for the weather to come back round.