It's a misty Wednesday morning, just before 10 o'clock. I'm eating a croissant with Kate Reid – the visionary behind much-lauded, perennially packed Lune Croissanterie – and I'm doing it all wrong.

We're at Lune's Russell Street store in Melbourne. True to the brand aesthetic, it's a dramatic, concrete-clad cubby with a line of city workers, tourists and die-hard regulars snaking out the door.

The moment I lift the croissant from its ceramic plate and – in hindsight, recklessly – rip off a corner, Reid stops me. An ex-Formula One engineer, she knows every second is critical.

"Can I recommend something? Try biting the ear off first. Pulling it, you're going to warp the layers. They're still warm in the middle. You're going to crush them and they're going to be doughy. Everyone always goes to tear a croissant apart."

It's very tearable, I counter, discarding the croissant's demolished right ear (a term for the small pointy end) and biting straight into the untouched left. Reid is right, of course.

This croissant came out of the oven less than 10 minutes ago. Compared with my usual technique of shovelling in flat, doughy shreds, biting straight in is a wildly different experience, one in which the crackly outer shell, silky inner layers and buttery air pockets all collapse in on each other at once. It's beautiful. I'm a little bit stunned.

I don’t think there’s any magic or science behind it. It’s just that we don’t cut corners.

Kate Reid

Reid laughs. "Please, go on tearing now."

To anyone not familiar with the Lune story, its meteoric rise could seem astonishing. Ten years ago, Reid was sleeping in a mezzanine above a tiny shop in Elwood where, almost immediately after opening, the very first Lune lines started forming around the block, some fans showing up as early as 3am.

Today, Lune is an unstoppable pastry powerhouse run by Reid and her brother, Cam. The siblings have five stores across Melbourne and Brisbane, two on the way for Sydney, and a cookbook hitting shelves this week.

"I don't think there's any magic or science behind it," Reid says. "It's just that, literally at every stage throughout the process, we don't cut corners. We care about every single detail."

Reid's day starts at 6.30am, when she walks her dog, Lily, to the Russell Street shop, then to the Fitzroy flagship. She checks the coffee is up to scratch (today: a little too milky) and always orders a croissant – she eats five a week.

Reid tries not to observe her customers but admits she cringes when someone asks for a knife and fork with a plain croissant – cutting and stabbing is even harsher than tearing. Then there are the rituals. The customer who painstakingly peels back the layers of a pain au chocolat, one by one, until only the chocolate batons and a couple of thin layers remain, ready to be rolled into a neat cylinder to eat.

The most horrendous crime committed against a Lune croissant, Reid says, was by one of her own team. A couple of years back, a staff member cut a croissant in half and filled it with mee goreng. "I looked at her and was like, 'I can't unsee that'. It's the worst thing anyone's ever done."

Reid is a purist, driven by precision, with an obsession that shines through in everything she does. This applies not just to croissants, but to every aspect of every store as the Lune empire expands.

When the Darlinghurst outpost launches next year (a Sydney CBD satellite will follow), all the Lune hallmarks will be present: benches made from poured concrete, designer LED lighting, pastry chefs on show. Service will be identical, as will the pastry line-up – a handful of cult classics like the Macca Sacca, a twice-baked number filled with macadamia frangipane and salted caramel, will be reinstated for the launch.

"It is going to be the most incredibly beautiful Lune store," Reid says. "In spring there's all the purple jacarandas flowering, it has this really wide footpath, it'll have great outdoor seating, it will be very European."

After breakfast, we head out onto the street, where Reid is being photographed for Good Food. "I think it's funny – when most chefs get photographed, they look quite serious. And whenever I get photographed, they're like, 'big smile!'," she says. "I don't want to have a huge smile on my face. I don't own a rustic little bakery. I run a medium-sized business. I drive a serious car. I feel like a serious person. I know my shit."

She confers with the photographer and they change tack (in the end though the grin wins out). Then, after snapping a few shots with her Porsche (Reid is an ambassador), she has the idea to move the shoot into the line of people waiting to get into the shop. Lines have always been part of Lune's makeup. At 10.30am the wait is about 10 minutes, which Reid says is the perfect length. Any longer and everyone – staff and customers – gets stressed.

The shoot attracts attention from fans who recognise Reid, their fingers moving across their phone screens with the tell-tale pinch of a stealthy zoom in. But ours is just one of multiple productions taking place. Inside, customers shoot content that'll soon slide into Lune's DMs.

Back at head office in Fitzroy, Reid flicks through them, firing off heart-eyes and fire emojis in response to striking shots of her creations.

Reid doesn't follow other pastry chefs on social media. "I'm not really interested in what other bakeries are doing," she says. "Even if it might have happened somewhere else, I'd prefer an idea to be really authentic, a genuine seed of inspiration."

Despite this, she knows she's sometimes too close to it all. But Reid's devotion can't be easily switched off. Last year, around the opening of Moon, an offshoot brand that sells crullers – glazed, circular choux pastries that are, like everything Reid puts her name to, outrageously good – the initial response wasn't always positive.

"People didn't understand what a cruller was. They were expecting it to be something croissant-related, and they saw something that looked like a doughnut. And then they took a bite, and it didn't meet either of those preconceived expectations," Reid says.

"The comments that were coming through on Instagram, not realising how much incredible hard work had gone into not only the building of Lune, but also Moon.

"And at that point, Cam's like, 'You take Instagram too personally. It's not a personal attack on you. It's someone just sharing their opinion without taking into account the person or the feelings behind it'."

Now, for the most part, someone else takes care of socials. Reid still writes posts but tries not to spend too much time reading comments or messages. Except last week, when she responded to a post by an 11-follower Instagram account, describing her croissant as soulless. "I couldn't help myself," Reid says. "Has she met me? Has she seen how much I care about croissants?"

Most days, the stores sell out by early afternoon. Despite the rumours, this is not the result of artificial scarcity. "If we could make more, while maintaining the quality, we would do so. But we're at capacity," Reid says. "You could easily make more by dropping the standard, but that's not Lune."

It's 1pm, and Reid's afternoon is wall-to-wall meetings. She briefs her front-of-house teams on the new cookbook and decides to switch wine suppliers for its upcoming launch party. The book launch is a momentous occasion. Up until now, the bulk of its offering has had a shelf life.

"I'll probably get a bit emotional," Reid says. "It's been a long time coming. A lot of publishers have approached me over the years. But it had to be exactly the right time in my life to do it.

"And when you're working 10- to 12-plus hours a day, you just don't have the time or energy to sit down and pen a book. I also feel like until now Lune didn't have enough of a story. But I'm very proud of it."

It's a good-looking book, in signature Lune black with an iridescent crescent embossed on the cover. Inside is a croissant recipe Reid developed specifically for home cooks, a pared-back version of the Lune dough (which requires special machinery). This one still takes three days to make, though, and it's hard work – one step begins with "set your alarm for 2am".

Reid no longer develops flavours herself. She's handed the reins to her kitchen team but remains the gatekeeper – she wants them to feel free to be creative, but there's a fine line between what's Lune and what isn't. Flavours should surprise and delight, and are often inspired by nostalgia and childhood memories, such as Wagon Wheels or Reid's mum's chocolate chip cookies. They should be able to be eaten by one person – so not too rich or too sweet.

And with the expansion, as the menu is identical in all stores, temperature and humidity must be taken into account: a pastry developed in Melbourne has to happily sit on the counter in Brisbane without flagging. I ask if the mee goreng variation ever stood a chance. "You know what? Maybe one day I'll surprise everyone with the mee goreng croissant."

Lune's playful flavour profiles have people flocking to stores, including celebrities such as Yotam Ottolenghi, a long-time fan. Reid loves that he lined up at the Fitzroy store himself (most high-profile visitors will send someone to pick pastries up for them).

But that anticipation – standing outside with other devotees while the scent of butter imported from Normandy drifts through the air, increasing in intensity the closer you get to the front door – is a quintessential part of the Lune experience.

"If you've worked hard for something, it always tastes better," Reid says. "It tastes sweeter."

Lune: Croissants All Day, All Night by Kate Reid, photography by Pete Dillon. Hardie Grant Books, RRP $55.