As I wander down a dark, narrow street in Gràcia, one of Barcelona's northern neighbourhoods, I am not sure that I'm in the right place. Then I spot a strange scene that assures me I haven't taken a wrong turn. Through a townhouse's wide glass doors, I spy six expectant-looking people sitting around a long table, while a man at the back is carefully arranging a row of plates on a makeshift bar.

"Is this EatWith?" I ask tentatively, but I already know the answer.

Dining in unusual places with people that you've never met is what Eatwith.com was invented for. The website is an online directory of supper clubs: anyone can apply to be a host, in their home or a venue of their  choice, and anyone who pays a small fee can attend. Founded in Tel Aviv, the site has had an incredible first year, expanding to feature 20 countries, including the US, Japan, Brazil and Italy. But it's in Barcelona, the official launch city, that it is the most active, with an astonishing 200 hosts. And so this is where I come to give it a trial run.

Earlier, after logging in and browsing the options on the website, I'd found myself drawn to the idea of a chocolate-themed night. Although most events take place in people's dining rooms, this one proves slightly different. The ground floor of the house has been transformed into an events space by Miquel, a thirtysomething, self-taught artisan chocolatier. Whitewashed walls cocoon an interior that's almost empty, bar a few well-sourced pieces of vintage furniture – an old fridge here, a hefty chest of drawers there.

The online description was a little vague ("It's just creativity and madness!"), so I'm not sure what to expect. What I get is a remarkably imaginative, multi-course tasting menu. First: a smooth chocolate fondant, covered in a lightly whipped carrot mousse. Next: tender ravioli, filled with lentils and chocolate, in a miso broth. It's weird but it works. Both dishes are perfectly executed, attractively presented and surprisingly moreish. And the meal costs me just £13 – about the same as a tour of the Sagrada Família.

Miquel says EatWith – which takes 15% of what each guest pays – is serving him well as he tries to build up his business of making and, he hopes, exporting chocolates. "People ask why I don't just get customers off the streets," he says, "but I like the flexibility. I like the characteristics of the people it brings. This is not a shop. I am not looking to compete with normal chocolatiers."

Although EatWith originally set out to target tourists, the biggest uptake in locations all over the world has come from locals. My fellow diners all live in Barcelona, despite originating from places as far-flung as Mexico, Sweden, Canada, France and Italy. Two of them are EatWith hosts themselves: outgoing Andrea, the Italian, hosts pizza parties in his back garden, and Monica, a firecracker from Mexico City, holds Mexican/Syrian food nights, to reflect her own mixed heritage.

Underpinning the site is an idea that everyone should have some sort of USP – be that the cuisine, the theme or the setting. To keep standards up, EatWith approves all its hosts, and those wanting to gain an additional "verified" badge can also be visited by an inspector, who will check their menu, venue and interpersonal skills. Some would say supper clubs should be more of an underground network, operating without a middleman but at least this site is taking responsibility, and offering its hosts support and, in some places, informal training.

Over the course of my weekend, I try two other EatWith dinners to get an idea of the variety on offer. One night I find myself in a fully open-plan apartment belonging to Xabi, a professional chef who has worked in Michelin-starred restaurants. He was running supper clubs and cookery classes before EatWith but the site has given him a wider reach. He serves a six-course menu (£43pp including wine), ably assisted by a grandmotherly type called Àngels, who squeezes my arm as she sets down every dish: potato ravioli with truffle mayonnaise and rusiñol (a local mushroom), and suquet (Catalan fish stew) with fennel confit.

My final meal is with a young couple, Vanessa and Renato, who offer a night of traditional Catalan food in their one-bedroom apartment in the city centre. Here, we dig into delicious esqueixada de bacallà (salt cod with tomatoes, onions, olives and vinegar) and fideuà, a Catalonian paella made with noodles. Before all this we try drinking wine out of a porró – those traditional glass carafes with a spout you hold above your mouth, moving your arm further and further away as your pour. It's an ice-breaker with a difference and I last about three seconds before dribbling down my front.

Vanessa and Renato's dinner is also unlike the others because they join us to eat, rather than just serving the food. We sit surrounded by their books and travel photos and, as there are just two other guests (both Barcelona residents), it feels like I've popped round to a friend's house for dinner.

I'm not sure how the evenings pan out in other countries but here the sobremesa (after-dinner conversation) at each event lasts for hours, and I wonder if I have just lucked out with particularly fine company. However, the early days of a peer-to-peer site are often the glory days, so if you're considering it, now's the time to try EatWith. It's no more of a gamble than any restaurant – and could be far more entertaining.
• More details from EatWith.com. Flights were provided by EasyJet (easyjet.com), which flies from seven British airports to Barcelona from £54 return. Accommodation was provided by peer-to-peer rental site Wimdu.co.uk, which has an 1870s apartment in Barcelona sleeping eight from £111 a night

Feed me: more EatWith dining experiences

Sushi making: Tokyo, Japan
Shino will not only make you sushi in her home – she'll take you to the market first to buy fresh fish and then let you help her roll the sushi out.
• eatwith.com/#!/offering/1586, £35pp

Feijoada chic: Rio de Janeiro, Brazil
Get a homestyle taste of Brazil's traditional feijoada (black bean stew). Host Alessandro serves it with a caipirinha and an optional after-dinner walk to Morro da Urca, for views of Sugar Loaf mountain.
• eatwith.com/#!/offering/4009, £21pp

Rooftop dining: Tel Aviv, Israel
Nurit whips up a feast from market-fresh ingredients and serves it on her roof terrace, overlooking the Yemenite quarter. Don't miss pumpkin kebabs on a cinnamon stick with tahini.
• eatwith.com/#!/offering/9288, £25pp

Whiskey Wednesdays: Los Angeles, US
After kicking things off with a whiskey cocktail, Kara serves a three-course meal of foods from her local farmers' market – sometimes in aid of non-profit charities.
• eatwith.com/#!/offering/3797, £21pp