Blame it on Nobu, that Japanese chef so beloved of fashionable diners.

Within a decade of him taking a humble, inexpensive and, some would say, unremarkable fatty fish and giving it an extraordinary treatment, he has single-handedly created a world market for black cod.

And it is not just for the sushi crowd — this new addition to top fishmongers’ slabs is now making an appearance at simchahs.

“When we serve it as part of a mixed starter, it’s always the star of the plate,” says Sarah Taylor of kosher caterers Tony Page.

“It’s really popular for barmitzvahs and batmitzvahs,” adds Zoe Lichman of London pan-Asian restaurant Gilgamesh.

So what makes a fish which Nobu London’s chef, Hari Shetty, admits is frankly less than flavourful, so popular with the Jewish community?

“Because it’s not very fishy,” he suggests, recalling all those dinner party guests who make this dubious attribute a pre-condition of serving a fish-based main course.

But non-fishy cod? The fact is black cod is not cod at all, but sablefish. It is always wild, and comes from the deep Artic seas where Alaska and Russia meet.

For years only the Japanese bothered with sablefish (the origins of how it suddenly changed its name are obscure), but the Alaska Seafood Marketing Institute recently introduced it to the British market, and it is now to be found at Harrods, Selfridges, Whole Foods and some branches of M&S, as well as one or two independent fishmongers.

But beware — it takes careful handling and flavouring to make this most delicately textured fish really sing on the palate. Thorough rinsing is vital, says Shetty, and only fish bought professionally filleted can be guaranteed free of the tiny pinbones (as I found to my cost with a piece boned at home).

The fillets cook within minutes to juicy perfection, falling into soft flakes, but the challenge is pairing them with a strong flavour, and the most natural partnership is with miso and other Japanese ingredients.

Shetty explains what is behind the laborious preparation of the black cod with miso which has become Nobu’s signature dish. “We marinate it for a long time in a mix of white miso paste with mirin [rice wine] and sake, which actually helps reduce the moisture and dry it out,” he says.

“Then we cook it on a griddle, which causes the sugars in the marinade to caramelise, making a delicious coating for the fish.”

You can find the recipe from the restaurant’s cookbook on the internet. North Londoners can source white miso paste in Japanese supermarkets in Finchley and Burnt Oak.

Not living near those areas myself, I had to make do with a recipe using miso soup mix. It yielded a brothy dish with a very pleasing texture and flavour. The fish also worked well poached in milk and served on a bed of risotto enriched with white wine, saffron, Parmesan and peas.

The good news is that, despite the eye-watering price of up to £35 per kilo, black cod, unlike its more humble namesake, is thoroughly sustainable.

Black Cod in Miso Broth with Noodles

Serves 2

Ingredients
● 4 tsp miso powder
● 2 tbsp Kikkoman teriyaki or soy sauce
● 1 sliced and de-seeded red chilli
● 4 shredded spring onions
● 75g thinly sliced mushrooms
● 1 pack stir-fry vegetables
● 250g ready-to-use udon noodles
● 15g butter
● 1 tbs toasted sesame oil
● 150g flllets of black cod
● To serve: sweet chilli sauce (optional)

Method
● Put miso soup powder in a wok or large saucepan, add 500ml water and 2 tbsp teriyaki sauce or soy sauce. Bring to boil, then reduce heat and add the red chilli, spring onions, sliced mushrooms and stir-fry vegetables.
● Simmer 5 minutes, add udon noodles and simmer another 5 minutes
● At the same time, heat 15g butter with 1 tbsp toasted sesame oil in a frying pan and add flllets of black cod, searing over high heat on each side. Turn heat down and cook a further 5 or 6 minutes till fish is opaque and flakes easily.
● Ladle noodle mixture into wide bowls and top each with a cod fillet.
● Serve at once, with sweet chilli sauce on the side.