Rocksalt, 4-5 Fishmarket, Folkestone, Kent

There's an almost fairy-tale quality to this week's story. Think of it as Local Hero with a side order of duck-fat chips. The cast: a philanthropic millionaire with a dream, and a brilliant young chef, escaping from the palace kitchens to start a new, simple life at the seaside.

The millionaire is Roger de Haan, who made his fortune by building up and then selling the Saga financial and travel group, founded by his father in Folkestone, where the company is still based. In the true spirit of Saga, de Haan didn't slump into passive retirement. Deploring the doldrums into which his home town had sunk, he invested millions in regenerating Folkestone's run-down Old Town, rebranding it as a cultural quarter with its own triennial arts festival and filling derelict shops with galleries and interesting small businesses.

In what he has described as a "moment of madness", de Haan also bought Folkestone harbour, a neglected afterthought to the town since the cross-channel ferry stopped running. The first part of his planned redevelopment, a destination restaurant, has just opened. Which is where our chef enters the story – Mark Sargeant, the Michelin-starred boy wonder of Claridges, and Gordon Ramsay's bright-eyed TV lieutenant, often seen chopping and cooking in the background while his boss shouted at people.

Having escaped from Gulag Ramsay, Sargeant has returned to his native Kent, trailing clouds of goodwill, and joined forces with de Haan's son, Josh. Their joint project, Rocksalt, a stunning, purpose-built restaurant on the harbour, is bankrolled by the de Haan millions. You've heard of the Aga saga. Well this is the Saga Aga.

Viewed from the shore, Guy Holloway's building is dramatic, clad in undulating black timber and looming over its scraggy surroundings like an intergalactic fishing hut. Inside, it's pure Californian harmony; a restrained, curving dining room lined in dark wood, with one glass wall offering a glorious panorama of the harbour, the sea a startling Mediterranean blue.

It took us a while to figure out that the colour is an illusion, created by a tinted glass balcony. But it works. There was an excitable, captain's-table buzz in the room, packed on a midweek lunchtime.

I'd assumed, given Rocksalt's position, that it would be a fish restaurant, but though there's plenty of seafood on the long menu (much of it from local day boats), equal space is given to local meat and poultry. Sargeant has clearly researched his market, and kept things relatively straightforward. For every smoked coley brandade, there's a smoked mackerel pâté, and the Josper charcoal oven turns out a variety of steaks, as well as baked mussels and grilled sardines.

We began with a pale and delicate taramasalata with good sourdough, and some Faversham oysters, and stayed fishy for our starters proper. Potted crayfish tails were fresh, rather than from a jar, according to my astute guest Tessa, with a chilli heat to the spiced butter. But my 'red herring' – beetroot-cured smoked mackerel – worked better as a concept than a dish, the alarmingly ruddy flesh oversalted and dry.

Monkfish, one of several 'catch of the day' main-course choices, came arranged in pearlescent slices over buttery peas braised with lettuce and lardons; it's hard not to love anything served with braised peas. But an otherwise decent sirloin steak was let down by its fixings – a half head of garlic not quite roasted to full sweetness, and the 'Rocksalt steak sauce', brown and sickly, which only a full DNA test could have differentiated from HP. Duck-fat chips lacked crunch and salt – scandalous, in a place named after the stuff.

Chocolate fondant gets a maritime twist, with a liquid centre of sweet-sharp sea-buckthorn. Gypsy tart, the Kentish answer to dulce de leche, is made to a recipe from Mark Sargeant's mother; the caramelish filling here whipped to a foamy lightness, nothing like the dense school-dinner version of blessed memory.

Service is still rather shaky, but small wonder if the staff were on edge; the place was crawling with food bloggers, as well as various multi-generational groups who turned out to be members, according to our waitress, of "The Family". They looked dead chuffed, and why wouldn't they? As family businesses go, a chic seaside restaurant is a lot sexier than selling discount travel insurance.

Mark Sargeant's dream of making Folkestone "the next Padstow" seems ambitious on the strength of one restaurant, but there's the additional draw of the art scene (the Triennial has just started) and the high-speed railway link from St Pancras, which puts the town within an hour of London. Even if some aspects of our meal spoilt the promised fairy-tale ending, Rocksalt is still a pretty fantastic restaurant. That distant creaking sound we heard wasn't wind in the rigging. It was surely Folkestonians getting down on their knees to give thanks.

Rocksalt, 4-5 Fishmarket Folkestone, Kent (01303 212070)

Food
Ambience
Service

Around £35 a head before wine and service

Tipping policy: "Service charge is 12.5 per cent discretionary, of which 100 per cent goes to the staff; all tips go to the staff"

Side Orders: Cream of Kent

The Smokehouse

Mark Sargeant's other new venture is this upmarket fish and chip shop nearby Rocksalt which has just opened and specialises in sustainable species.

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