The po’ boy is the most overrated sandwich on the planet. There, I said it. And now I can never go to New Orleans again, lest I want to get clubbed to death with day-old baguettes. Let me explain: I was in the Louisiana city two years ago, when I perched myself at the restaurant bar in my hotel and ordered a po’ boy, my first one ever. As I bit in, I noticed the bread was on the stale side and the fried shrimp was flavourless. The iceberg lettuce was flaccid and the tomatoes were mealy. The baguette had only a minimal amount of mayo, barely keeping me from feeling like I was eating a drought. The supposedly edible pride and joy of the Big Easy was a big let down.

My sandwich-loving friends gave me sideways glances when I told them about my experience. They had theories: I’d gone to the wrong place; I didn’t do enough research to find the best po’ boy in town; I was an imposter of a food writer. At least two of these three theories seemed plausible.

But recently I was back in New Orleans, suspiciously eyeing anyone wielding a firm baguette, and decided to give the po’ boy another shot. After all, a French stick crammed with fried oysters or shrimp, lettuce and tomato can’t be so bad, right? This time, though, I was going to do my research.

The po’ boy – at least the name – came into existence in 1929. That’s when there was a strike among street car workers, specifically the Amalgamated Association of Electric Street Railway Employees, Division 194. It went on long enough that the strikers began to grow weary – and hungry. This is where brothers Bennie and Clovis Martin, former street car workers who’d opened a coffee shop in New Orleans’ French Market, enter into sandwich history. They sympathised with the strikers, and spread the word that any striker could come by the shop for a free sandwich. “These are for our po’ boys,” one of the brothers said, referring to the striking workers. The sandwich they were giving away was made up of just lettuce and tomato or scraps of meat, depending on who you ask. Whatever the case, the name stuck and the po’ boy was born.

Today, traditional po’ boys consist of fried shrimp, fried oysters or roast beef, along with lettuce, tomato and mayo. But here’s where things get really confusing: in New Orleans the term ‘po’ boy’ has become synonymous with any ‘sandwich’ made with a baguette. With such broad strokes, what, I wondered, was the real definition?

It gets to a point where it’s just a literal hot mess

My first stop on the Nola po’ boy circuit was Parkway Bakery & Tavern. Established in 1911, Parkway serves up the triumvirate of traditional po’ boys. But it’s their roast beef that makes the place renowned. Justin Kennedy, whose family owns the business, took me into the kitchen to show how they simmer and stew the beef for hours. “It gets to a point where it’s just a literal hot mess,” he said, taking the lid off a giant pot of what looked like delicious brown sludge. “We call it debris. A good roast beef po’ boy should have juice running down your arm by the time you’re halfway through.”

True to his word, my arms were dripping with beef gravy when I tucked into a sandwich. The beef was rich in flavour and had a texture that melted nicely into the ultra-soft bread.

“But it’s not even about the beef,” Kennedy told me. “The real clue to what makes a po’ boy is the bread. It has a uniqueness to it that you’d be hard pressed to find anywhere else.” He pointed at my half-eaten sandwich. “It’s flaky and crusty on the outside and really soft and nearly hollow on the inside.” He was right: the interior of the bread had the consistency of cotton candy. It’s really the perfect bread because it doesn’t overwhelm the sandwich and therefore lets the ingredients speak for themselves.

“I’ve taken this bread out of state to do functions. And this might sound like a bunch of BS, but the bread changes. It’s not the same when you take it out of the area,” Kennedy said.

I asked Kennedy if that means you can never eat a proper po’ boy outside of New Orleans.

He shrugged and then offered: “I don’t want to take anything away from anyone trying to make a good po’ boy elsewhere… but yeah, it kinda seems that way, doesn’t it?”

So, I wondered, what is it about the bread? To find out more, I met up with Jason ‘Rosie’ Flato, a chef at M Bistro in the Ritz-Carlton hotel. Besides the fact that Flato is a po’ boy fanatic, I wanted to see what an upscale version looked like.

“It’s all about the bread,” Flato said right away, as we sat in the restaurant’s dining room. “That soft, chewy interior and crisp exterior? You’ll never find bread like this anywhere.”

That soft, chewy interior and crisp exterior – you’ll never find bread like this anywhere

While others like Kennedy say it has a lot to do with the climate and humidity of New Orleans, Flato believes it’s the technique. “When you look at the recipe and ingredients, it’s no different from anywhere else. Yeast, salt, water, flour. It depends on how long you let it sit. It’s proofed – or let to rest – longer here than other places. We proof it for 12 hours and then punch it down and then let it sit another 12 hours. Then it’s baked. That’s what makes our bread unique.”

And there’s a reason why the po’ boy solely uses the baguette. Before the famed street car workers went on strike, the baker who supplied the Clovis brothers (and many others) with bread made oval-shaped loaves, which created different sized sandwiches depending on what part of the loaf the bread was cut from. As a solution, the baker began making baguettes so every street car worker would get an equal-sized portion. The bakeries Leidenheimer and Alois J Binder soon followed suit. Today these three bakers – Gendusa, Leidenheimer and Binder – are still the main bread suppliers to po’ boy shops throughout New Orleans.

A minute later, Flato’s po’ boy was sitting in front of me. I picked it up and bit into it. The fried shrimp burst with flavour. The lettuce added a crisp texture, the tomatoes a hint of acidity. And there was a surprising smokiness to the sauce slathered on the inside of the bread.

“This is a cross between staying traditional and being modern,” Flato said. “I go super traditional, not touching the structure of the po’ boy so I can show off the bread and the shrimp. You have to respect the history behind it. But I put a twist on it by adding a barbeque aioli instead of the traditional mayonnaise. The sauce helps to brighten the seafood.”

I thought back to that flavourless shrimp po’ boy from two years ago and my opinion of the sandwich had definitely been revised. This one was outstanding.

You can have traditional po’ boy ingredients between two pieces of sliced bread but it’s not a po’ boy, but if you have that New Orleans baguette, it’s a po’ boy

This being 2017, if there’s a traditional and an elevated version of something, there’s got to be a hipster version. Meet Killer Po’ Boys, a French Quarter sandwich shop that started in the back of an Irish pub and is now one of the city’s favourite po’ boy shops. With a menu listing a sweet potato po’ boy, a glazed pork-belly po’ boy and a chorizo po’ boy, the shop definitely takes advantage of that broad definition of what a po’ boy is – which owner and chef Cam Boudreaux told me is anything inside that now-famous New Orleans baguette. You can have traditional po’ boy ingredients between two pieces of sliced bread but it’s not a po’ boy. But if you have that New Orleans baguette but non-traditional ingredients, it’s a po’ boy.

Case in point, Boudreaux said his sandwich obsession started with the banh mi, or Vietnamese po’ boy as it’s known locally, stuffed into a baguette.

“I was really inspired when I saw the Vietnamese po’ boy, seeing that there can be other types of po’ boys outside of the traditional,” he said. "In fact, our shrimp po’ boy uses all the ingredients of a banh mi: daikon, carrot, coriander. But we put gulf shrimp in it instead of pork, thus combining elements of Vietnamese cuisine that has been very influential here, and traditional New Orleans po’ boy ingredients.”

You wouldn’t know it if you only visited the French Quarter, but venture around New Orleans and it’s clear that the Vietnamese have made a huge contribution to the city in recent decades. When thousands of southern Vietnamese fled their country after the war in 1975, many Vietnamese immigrants were attracted to Louisiana because it was like south Vietnam: the humidity, the delta, the rice-growing culture, and, of course, the leftover aspects of French colonialism that have shaped both cultures. It’s no surprise that residents of New Orleans – Vietnamese descent or not – are highly influenced by this Southeast Asian culture.

Which brings us to the very latest incarnation of the po’ boy, the Vietnamese ‘pho boy’. I encountered this edible miracle of a sandwich – made with all the ingredients of pho, Vietnam’s national noodle dish (minus the noodles), served alongside a bowl of pho broth for dipping – at Namese. Though no longer on the menu, I found something similar at the Nola-based food truck Saigon Slim’s.

“We translate a lot of Vietnamese flavours into po’ boy sandwich form,” said Saigon Slim’s co-owner and chef James Paul, who got his cooking chops at French Quarter staple Arnaud’s plus his aunt’s two Vietnamese restaurants in the Bay Area. The pho boy sandwich was not on the menu – chef Paul only makes it in the winter – but he also serves up something similar: the Pig Shrimprin’ po boy, which takes all the ingredients of a Vietnamese summer roll – shrimp, mint, cucumber, peanut sauce and pork – and stuffs them inside a soft baguette made by Vietnamese bakery Dong Phuong.

The po’ boy is one of the world’s great sandwiches

I finished eating at Saigon Slim’s, feeling incredibly satiated by my po’ boy crawl through New Orleans. And I can now say that my friends were right: I was badly misinformed about this iconic sandwich. The po’ boy is one of the world’s great sandwiches.

Join over three million BBC Travel fans by liking us on Facebook, or follow us on Twitter and Instagram.

If you liked this story, sign up for the weekly bbc.com features newsletter called "If You Only Read 6 Things This Week". A handpicked selection of stories from BBC Future, Earth, Culture, Capital and Travel, delivered to your inbox every Friday.