The story goes that after spending time in France, a Portuguese man named Daniel David da Silva returned home in the 1950s intending to bring back the croque-monsieur, a ham and cheese toastie topped with béchamel and more cheese.
However, da Silva adapted the recipe to Portuguese tastes and created the francesinha, which became a signature dish of Porto, in the north of the country. It's where Gloria Belinha, the founder of Sydney's Gloria's Portuguese Restaurant, had her first taste of the sandwich half a century ago.
Born in a small village 20 kilometres south of Porto, she began visiting the city with her family as a teenager. "On Saturdays, we always used to go for a movie, a francesinha and some beers," she recalls.
"I don't believe I had tasted chilli like piri-piri, until that time, in the sauce. Today you can have the sauce from mild to very hot, but at that time, all the sauces were the same with piri-piri. At 15 or 16, I tried that and I was 'Wow!' It was really nice and different."
Francesinha recipes vary slightly, but they always start with several types of meat piled between two thick slices of white bread. The most common are ham, minute steak and sausages like linguiça. The sandwich is grilled in a press, then fully covered in cheese slices and a tomato and beer sauce. A fried egg is often added on top, and chips are almost always served on the side.
"It's part of life, part of the culture, part of who we are in the north."
"What makes this special is the sauce," explains Belinha. "Many restaurants keep their sauce a secret, and only one person can prepare it.
"The base is tomato, but it can have alcohol like whisky or beer, different spices and piri-piri. When it goes on top of the sandwich, it melts the cheese, and the sauce on the bottom soaks the bread. You have to eat this with a fork and knife."
For the uninitiated, the francesinha might seem heavy. But in Portugal, it's often eaten as an afternoon snack.
"We'd have it for lunch or late in the afternoon because we have dinner very late in Portugal. After work, people stop at what we call a snack bar to have a francesinha. It's part of life, part of the culture, part of who we are in the north," says Belinha.
Since Belinha's teenage years, the sandwich has become popular in other parts of the country, but not as ubiquitous as in Porto and the surrounding towns.
When she moved to Sydney in the 1980s, she took her uncles' francesinha recipe with her. "In 1988, I opened my restaurant because coffee and francesinha were the things I missed the most from my country," she says.
She is now retired and Gloria's Portuguese Restaurant is run by her son Alcino. But the francesinha hasn't left the menu. It features ham, steak, sausage, chouriço, a fried egg, cheese, a slightly spicy tomato-based sauce, and a side of chips. Belinha says it's especially popular with young diners, who've either grown up with the dish in Portugal or who have been introduced to it by Portuguese friends.
While you could make a francesinha at home, she says there's nothing quite like having it out: "There's a different feeling when you have it at a restaurant or a snack bar.
"You can have a beer at home or a beer at a bar; it's not the same. It's like that with a francesinha, you want to have it out."
Traditionally, the soup, which was a staple in rural households, was little more than water poured over stale bread crusts, with an onion bulb added and the whole lot left to simmer for the day.