The plates have been cleared, the last of the red is gone, and nobody is quite ready to move. Outside it is properly cold now, the kind of dark that arrives at half past four and settles in for the winter. This is the exact moment the Irish coffee was built for. It is pudding, digestif and nightcap folded into a single warm glass, and one of the few drinks that can honestly end an evening and revive it at the same time.

It is also, like most simple things, quietly easy to ruin. A sloppy Irish coffee is a grim object: lukewarm, oversweet, the cream collapsing into a greyish slick, the whiskey either shouting or missing entirely. A good one is a small miracle of temperature and texture, hot coffee and cool cream meeting on your top lip, the sugar and spirit humming underneath. The difference between the two is technique, and there is far less of it than you think.

A drink with a flight attached

The Irish coffee was not born in a pub but in an airport, which is a more romantic sentence than it has any right to be. The year was the early 1940s, the place was Foynes in County Limerick, then the terminal for the great transatlantic flying boats. Passengers would stagger off after a long, freezing crossing, and the chef, a man named Joe Sheridan, decided hot coffee alone was not equal to the task. He laced it with Irish whiskey, floated cream on top, and sent it out. As the story goes, an American traveller asked whether he was drinking Brazilian coffee. Sheridan told him it was Irish coffee, and the name stuck to the drink for good.

From there it crossed the ocean it was invented to console. A San Francisco travel writer, Stanton Delaplane, tasted it at Foynes and talked the Buena Vista Cafe on Fisherman's Wharf into recreating it in 1952. They reportedly spent a long night watching the cream sink before they cracked it, and the Buena Vista has been pouring Irish coffees by the thousand ever since. Not bad for a drink that started life as first aid for cold passengers.

The four things, and the order they go in

An Irish coffee is four ingredients and one piece of technique. The four things are hot, strong coffee, a measure of Irish whiskey, a little sugar, and lightly whipped cream. The technique is the float, and we will come to it. Order matters more than you would guess. Warm the glass first with a splash of hot water, then tip it away, so the finished drink does not surrender its heat to cold glass. Add two teaspoons of brown sugar and a double of whiskey, roughly fifty millilitres. Pour over hot, strong coffee, leaving a couple of centimetres at the top, and stir until the sugar has completely dissolved. Then float the cream, and stop touching it.

The sugar is not optional, and not only because it sweetens. It is structural. The dissolved sugar thickens the coffee just enough to hold the cream aloft, which is why a sugar-free Irish coffee tends to end in a muddy collapse. This is the rare drink where cutting the sugar actively breaks the recipe.

The whiskey question

Here is where good intentions go astray. The instinct to reach for your finest single malt is generous and completely wrong, for the same reason it is wrong in a hot toddy: heat, sugar and coffee will trample all over the fine detail you paid for. What you want is a smooth, characterful Irish blend with enough backbone to be heard through the coffee and enough warmth to play nicely with the cream. Glendalough Double Barrel, aged in bourbon and then oloroso sherry casks, is almost purpose-built for the job, all soft vanilla, orchard fruit and a gentle nutty sweetness that meets the sugar halfway. You want a whiskey that flatters the drink, not one that fights it for attention.

If you want to gild the thing, and December is the month for gilding, a measure of Five Farms Irish Cream in place of some of the whiskey turns a nightcap into something closer to liquid dessert. It is softer, sweeter and unapologetically indulgent, the Irish coffee in its party clothes. Traditionalists will raise an eyebrow. Let them.

The cream, and why it floats

The cream is the one place the drink asks for a little care. It needs to be lightly whipped, barely thickened, to the point where it is just too heavy to pour in a clean stream but nowhere near the stiff peaks of a trifle. Double cream, whisked for ten seconds longer than feels necessary, is about right. Pour it gently over the back of a warmed spoon held just above the surface of the coffee, and it will settle into a cool white collar that sits there, serene, while the hot coffee waits beneath. Done well, you never actually mix the two. Each sip pulls hot through cold and bitter through sweet, and that is the sensation people remember long after they have forgotten what was in it.

The coffee, and the glass

The coffee has to pull its weight. Weak, stewed filter coffee makes a weak, stewed drink, so brew it strong and fresh, a good cafetiere or a long shot stretched with a little hot water. It wants to be assertive enough to stand up to the whiskey and the cream without turning bitter. As for the vessel, the classic is a warmed, stemmed glass with a handle, which keeps your hand off the hot glass and shows off the two-tone layering that is half the pleasure. A small heatproof tumbler will do at a push. What matters is that it is warm before the coffee goes in, for the same reason the whole drink lives or dies by temperature.

Last pour

So, back to the cleared table and the room nobody wants to leave. Warm the glass, dissolve the sugar, pour a smooth Irish blend and strong hot coffee, and lay a cool collar of cream across the top. It takes three minutes and a little patience with the float, and it gives back the most companionable drink in the cold-weather canon, equal parts pudding, warmth and good idea. If it leaves you in the mood for more, our notes on the hot toddy and the sidecar cover the other two drinks worth knowing when the nights draw in. But pour this one first, with the dishes still on the table and the cold pressing at the window, and you will understand why a chef in a draughty airport thought it worth inventing.