Do you want to go to 'paradise'?", grins Paul McFadyen, before ducking behind a towering stack of dusty wooden barrels. I'm not quite sure what 'paradise' entails, but, as I glance up at the cobweb-strewn rafters and around at the dimly lit barn, the tropical beaches and cascading waterfalls the word often evokes seem very, very far away.

We're in the depths of 'cognac country', about an hour and a half from Bordeaux, being led through one of the most important buildings on the Maison Ferrand estate by its spirits ambassador and Notting Hill bar owner Paul McFadyen. Despite appearances, we're not here for the aged eau de vie that makes this area of western France so special. We've got gin – yes, gin – on our minds.

In this unassuming, whitewashed building, the maison stores its most inventive spirits – and what McFadyen is most excited to show us is just up a set of creaky wooden steps. But first, a trip to the locked cellar is in order, because the story of how Maison Ferrand got into gin starts in paradise… Or paradis, if you're French and work with cognac, because in these parts that word refers to the ageing cellar where the estate's oldest cognacs are stashed away to gracefully mature with the passage of time.

We're in the depths of 'cognac country', but we've got gin –yes, gin – on on our minds

Waiting at the foot of paradis, in front of a cast-iron set of gates, is McFadyen. Beyond the bars, ancient-looking bottles glitter in the half light. "Some of these have been here longer than Alexandre," he says, audibly sighing at the sight of so many unusual and, in some cases, rare bottlings.

The Alexandre he is referring to is Alexandre Gabriel, our generous host and current proprietor of Maison Ferrand. Gabriel started working here – one of France's oldest cognac houses – in 1989. He came straight from Paris and was fresh out of business school. Back then Maison Ferrand's sales were next to dormant. Given the long-standing quality of the maison's cognac, though, it took only a little bit of effort (or so McFadyen tells it) to turn fortunes around. But Gabriel is a restless man: once things were on track and the collection of bottles behind the gates of paradis began to grow, he soon found himself wondering what else they could do with the estate.

Thanks to strict regulations imposed by the Appellation d'Origine Contrôlée (AOC), cognac producers are only allowed to distill between November and March; after that their stills must be locked up and put into hibernation for seven long months. Eager to innovate, Gabriel started experimenting with gin, specifically gin distilled in cognac stills – a method that was not only unheard of, it was outright banned. "I was trying desperately to convince the French government to allow me to produce gin at my cognac distillery," Gabriel tells us later that evening, once we've left the barn in search of a drink. "But no one in France had ever approached the government with this request."

Juniper fields

Juniper fields

It took five long years of intense negotiations before Gabriel finally obtained the AOC authorisation, and after that Citadelle Original was born. London Dry in style, it's made from a neutral alcohol of French wheat washed with juniper, citrus and seventeen other botanicals. The result was a zesty gin smoothed over with almond, sugary aniseed, spiced pepper and cinnamon. It's perfectly balanced and makes a cracking gin and tonic, but the recipe itself wasn't exactly new: Gabriel had stumbled across this combination during his research; reviving the recipe (and, in fact, the Citadelle name itself) from the records of an 18th-century gin producer in Dunkirk.

What really set it apart, though, was the method of distillation. It's an obvious point, but one worth making: alcohol and an open flame don't mix. Instead, Most producers opt for steam coils or jackets to set off all those vital chemical reactions. But not Citadelle – the very cognac stills that Gabriel had petitioned so hard to use were the exact thing that brought such a distinctive flavour profile to the gin. After progressively infusing all the botanicals, the team lightly filtered the liquid before heating it over a flame-fired still. With tiny bits of citrus peel still floating around, the spirit underwent what is known as the 'maillard reaction'. That's the same reaction responsible for making steak or freshly baked bread smell and taste so delicious. In this case, once the heat had built up to a hefty 1,000°C, the sugars in the alcohol started to caramelise. This last step was responsible for creating the unique taste and mouthfeel of Citadelle gin that is familiar, but exotic; traditional, but modern; distinctly French, and all the more delicious for it.

Gin was thought of as the starting point for greater things – not a spirit celebrated in its own right

There's no doubt that Gabriel's efforts had paid off, the only problem was, back in 1996 gin was not the furiously popular tipple it is now. In the 1990s, concerns about provenance, aromas and bouquet (topics you so often hear gin enthusiasts like McFadyen frequently talk about now) were not often heard outside the world of wine or whisky. Citadelle's distillation method and its 19 botanicals were seen as absolute 'fluff'. Remember, this was the era of cosmopolitans and appletinis; no one really paid much attention to the French producers doing away with tradition and firing up their cognac stills just as everyone else was packing down for the summer. Gin was thought of as the starting point for greater things – not a spirit celebrated in its own right.

But come 2009 that all changed. Ferran Adrià of El Bulli fame declared drinking gin a "gastronomic act" and shared his recipe for the perfect G&T. His gin of choice? Citadelle, no less. From then on, sales skyrocketed, going from almost nothing to a million, seemingly overnight. Citadelle Original was in vogue – and suddenly winning awards left, right and centre. Yet, if anyone thought Gabriel was about to slow down, content to ride that single wave of popularity, they were very much mistaken.

Only the year before he'd started experimenting with an aged gin. What started as some family fun soon transformed into Citadelle Réserve, a golden-hued spirit that's aged in five different wooden barrels over the course of five months. The Réserve came to be known as Citadelle's spicier, more herbaceous sibling; pulling in top honours at the San Francisco World Spirits Competition World Spirits Award, The Gin Masters and more. But what made this spirit stand out from the rest wasn't the three extra botanicals or the fact it was left to rest. Gin, after all, has been aged since the dawn of, well, gin-time. It was how the Réserve was aged in the final stages of its journey to the bottle that really captured people's attention.

Back at the barn, McFadyen playfully calls for us to "Come on!" before he bounces up its creaky wooden stairwell. We follow, huffing ever so slightly, and by the time we reach the top he's already sprung across the floor and is now leaning nonchalantly against a giant wooden egg. Around him, the entire year's supply of Réserve is ticking away.

"It's good, isn't it?", he says, running his hand down the side of this great, big, polished beast. This is the grand reveal: the 8ft-tall reason why Citadelle Réserve stands apart from its competitors. During the final few weeks of aging, the gin is fed through the egg. "Citadelle is the only gin distiller in France to use this technique to age its gin." Explains McFadyen. "The shape is super efficient. It creates a natural convection, so the gin is in constant motion."

McFadyen calls it "dynamic aging at its best," and I believe it. I also believe him when he points out that the French cooperage behind this £25k egg-shaped ageing cask only make four 'barrels' a year. It can't be easy making something this complex. Nor, as I come to realise, is it surprising that Citadelle would be the driver of such an unusual method. Since its inception, the story of Citadelle and all its variants has been far from simple. But in a way, perhaps that's what makes this gin so special. And despite its boom (and continued growth) in popularity, production is still relatively small – because the last thing the team wants to do is compromise on quality.

"Distilling is the act of creating emotions in a bottle," says Gabriel as he passes around more drinks later that evening.

"To compromise on quality would be to settle for less." Which is also the reason why, he explains, Citadelle doesn't adjust its recipe or ABV for export. Whether you were sipping on a martini in London or saying salud with a round of G&Ts at El Bulli, your Citadelle Original gin always would – and always will – come in at 44%, while the Réserve will make itself known at 45.2%.

Citadelle Gin

The makers of Citadelle suggest keeping things simple in their signature serve with nothing but lemon, tonic and ice added to the gin (oysters on the side optional, but recommended) 

Maybe that's why Ferran Adrià took such a shine to it. A strong drink after service will always go down well, after all… "Well, maybe," says McFadyen when I propose the idea. "Alcohol is a solvent and the higher the proof, the more flavour you carry. Changing the recipe or watering down the ABV changes the taste. It basically creates a whole new drink." And, as Gabriel points out, they can't have that: "To change the proof for every market would acknowledge that Citadelle is not the perfect gin for everyone."

Perhaps it's the gin talking, but I can't help agree. It is pretty much perfect, and without the complicated distillation process and all its unique blend of botanicals and that giant egg-shaped cask, Citadelle would not be the same delicious spirit it is now.

But just because he has us convinced, does that mean Gabriel is ready to set back and settle for that? Not a chance. The next day, as we're gingerly packing up our stuff ready to roll off the estate with our hangovers in tow, we spot him poking around in a field across the way. Not long ago, Citadelle's team cleared some acreage to plant the first juniper bushes on the estate. Gabriel's gaze might be scanning the ground now, but he never takes his eye off the future.