The story of Prawn On The Lawn is one of constant ingenuity. It started out as a tiny North London fishmonger and seafood bar; just eight seats, a fish counter and no fryer. "The idea was, you could have a glass of fizz and a few oysters while you bought your fish and it was being prepped," explains Katie Toogood, who runs POTL with her husband, self-taught chef Rick.

The tricky bit was, they didn't have a licence for hot food. "It forced us into doing something a bit more out there," admits Rick, describing how their ever-changing menu revolved around curing, pickling, ceviche, oysters, and crab and lobster on ice. "Having all the fish on display, we just wanted to cook it. As a chef it became quite frustrating."

Five years on, the pair have swapped their stripped-back fishmongers for two restaurants - one in London and one in Padstow, Cornwall - and now have their own self-titled cookbook, packed with 'fish and seafood to share'.

They do seafood without sticking to rigid rules

They might have fryers at both locations now, but don't expect to find them dishing out portions of salt and vinegar-covered cod. "We don't do fish and chips," says Katie, "[but] we could do you some crushed new potatoes and tempura battered white fish."

Instead, they're all about small, inventive sharing plates - swayed by whatever their Cornish fishermen have hauled in that day. Rick, who previously worked front of house for a string of high-end restaurants, had never been particularly interested in plodding through meals that predictably went: starter, main, dessert. "We loved the idea of sharing, it's how we both grew up," he says, as Katie chips in: "Everything in the middle of the table, helping yourself."

They also wanted to smash up the idea that seafood restaurants should being excruciatingly formal - it's fiddly enough cracking crab claws without worrying about how smart your shirt is. "When you go to Europe, seafood is so informal," muses Katie. "It's just stuff off a boat, and real basic cooking."

When the pair met online ("It wasn't on Plenty Of Fish," says Katie with a laugh), she didn't really eat meat and was "way more scared of fish". Rick sorted that out.

The recipes blend food with memory

"I don't know when I became so obsessed with fish," he says, slightly bemused. "I was born in Guernsey, but left when I was three or four, but mum says whenever we'd go to the market, I'd go straight to the fish counter and she couldn't tear me away." These days, they're both obsessed, and Rick's recipes are laced through with memories of their tastiest seafood adventures.

"We caught some trout, then out of nowhere this fisherman produced an avocado, chilli, a few limes and a bag of tortilla chips. We filleted the fish, made this amazing trout ceviche and just sat in the middle of the sea and ate it," says Katie, remembering a boat trip in Mexico last summer.

They later recreated it on their Cornish fisherman Johnnie's boat. "You can pretty much do it with any fish," says Rick. Their whole red mullet, floured and deep fried, comes from sitting on plastic chairs with Rick's parents in a little bay in Greece, where the fish was served with really good olive oil and some lemon juice, whisked, and poured all over the fish. "The simplicity of it," says Katie reverently.

When it comes to fish, explore outside your comfort zone

While they're all about keeping things simple, they've noticed that people are becoming more adventurous with their seafood. So much so, "people don't even want cod if it's on the menu, they're like, 'No, have you got any pollock?'" says Katie. Some do still need to be nudged to have their fish whole rather than filleted, though. "You just get so much flavour from the bones!"

Hence why Rick has taken the decision that, if you order crab at POTL, it'll come whole, not dressed. "It's the theatre of it," he says proudly. "Picking the meat out is so rewarding." There are some things just don't need reinventing.

Prawn On The Lawn: Fish And Seafood To Share by Rick and Katie Toogood is published by Pavilion, priced £18.99. Available now.