'There are no rules': jaffles get wild in Melbourne and Sydney this winter, with curry, confit duck and more

• 20+ of the best toastie and jaffle recipes

What's in a name? When it comes to toasted sandwiches, a lot.

This winter you might see grilled cheese masquerading as a toastie, or a toastie billed as the more American "melt". But there's no mistaking the jaffle.

Defined by its firmly sealed edges and a puffed, bronzed middle that holds its treasure, the jaffle is being embraced once again by chefs, who are filling white bread with mac-and-cheese and other inventive additions not seen since 2015's jaffle craze. MasterChef contestant Minoli De Silva won a challenge with a chicken-potato curry jaffle in April.

"Don't be afraid. You can put anything in a jaffle," says O Tama Carey of Lankan Filling Station in Darlinghurst, Sydney. Every Saturday, the Sri Lankan restaurant offers a new variation, whether it's crab curry or mozzarella with acharu (pickle) and curry butter.

Even if Australians have our pick of bagels, focaccias and banh mi these days, the jaffle is hard to resist.

Many people consider it part of our national culinary canon, thanks to Sydney resident Dr Earnest Smithers inventing the first jaffle iron in 1949. It was replaced by Breville's square-shaped electrical appliance in 1974 and, since then, our jaffle fillings have progressed past tinned braised steak and onions

Mushroom ragu with truffle butter and smoked scamorza is offered at Sydney's Old Clare Hotel in Chippendale, while confit duck fills the sandwich at Her Bar in Melbourne's CBD. The jaffle suits oozy ingredients.

"Compared to a toastie, you're not losing any of that moisture. It stays inside," says Her Bar's chef Josh Rudd.

Flyover Fritterie in Redfern, Sydney, layers dosa-style potato with peanut chutney and coconut crunch, and Melbourne's Hardware Club recreates the cheesy, peppery flavours of cacio e pepe pasta sauce, using five types of cheese and frying the sealed sandwich after the jaffle is toasted.

Meanwhile, Parramatta's Meraki Merchants opts for sujuk (Turkish sausage), roasted capsicum and black olives, and Union Kiosk in Melbourne is an all-vegan jaffle shop.

It could be argued that the square sanger reflects our progress from a nation of meat-and-three-veg eaters to more cosmopolitan diners. But is the jaffle truly an Aussie innovation?

Nicola Dusi, chef at The Hardware Club, tried his first jaffle nearly a decade before he arrived in Australia, thanks to a grandmother who picked up a jaffle-maker in Verona, Italy. "I loved the crunchy edges," he says. "I was like where does this thing come from?"

Flyover Fritterie owner Gunjan Aylawadi was raised in Delhi and also grew up with jaffles. An old-fashioned iron heated over fire would cook sandwiches filled with last night's leftovers.

"It was a fantastic way for our parents to feed us," she says, adding that this was common among people who grew up in India in the early 2000s.

Ex-pats love the taste of home Flyover offers via its bready pockets of paneer tikka or chana masala.

"We have a lot of fun with our food, so there's no rules," says Aylawadi.

Don't mess with the bread, though. Every chef recommends a basic sliced-white.

Although she makes her own bread for Lankan's jaffles, Carey says it is based on Sri Lanka's answer to Tip Top, kade paan, which means "shop bread".

Cheese choice is also critical. Carey recommends a mix of buffalo mozzarella and cheddar ("you get oozy cheese and cheddar gives it that nice stringy thing") while The Old Clare's Jarrod Walsh says scamorza works because "it's something stretchy that will melt really nicely". Rudd uses Comte cheese for his French-inspired sanger – it's on theme but also melts well.

Overfilling a jaffle is definitely possible, but there's some debate on whether that's a problem. Aylawadi purposely overfills Flyover's sandwiches so that the sauce oozes and creates caramelised edges. However, Walsh recommends leaving a one-centimetre border on all sides when assembling.

The best advice for jaffling might be from Rudd: "You can't really go wrong between two bits of bread and some cheese."