If you pass the big, bold restaurants around Berkeley Square, and nip through a gap between the Bentleys idling on Berkeley Street, you’ll find a subtle awning on Hay Hill that marks the entrance to Japanese restaurant Nijū.

The homestyle Japanese menu, designed by Endo Kazutoshi and executed by Chris Golding, has rightfully garnered praise in the past year – the sharing platters made by Polish-Japanese-British sushi chef David Bury tend to be politely fought over. In the basement, though, is one of the best bars to open in London in recent years, under the direction of Angelos Bafas. 

Nipperkin’s quiet confidence begins on the street, where a small brass plaque announces its presence. The bar space itself is only a place to see and be seen because it is so intimate – with fewer than 20 seats. 

This is because it is based on Japanese listening bars, explains Bafas: ‘Japanese listening bars, or kissa, developed in the 1950s. They started out in people’s living rooms. It was because vinyl from the west was hard to get hold of. So, the audio geeks, DJs and so on who had great sound systems and the records to play, would gather their friends in a small living room to listen to jazz from the States, then soul, funk and so on. And bars grew out of that tradition. We’re inspired by that; we can bring people together around the central table and enjoy nice tunes and nice drinks.’

It is indeed jazz, funk and soul that creates a soundtrack (at a lower volume than those original Tokyo audiophiles played), with the current record – the bar team bring in their own classic albums (Guru’s Jazzmatazz Volume 1) or rare finds (Singaporean prog and funk band Funkgus, anyone?) – displayed in the traditional way, next to the turntable.

The Japanese influence extends to the menu, too: ‘The whole idea is about seasonal and local products, using the best ingredients and produce we can find within the British Isles. But all the drinks have subtle Japanese touches. Many people wonder how we can achieve both local and Japanese, but we have wasabi grown in West Dorset, shiso leaves grown in Norfolk and sansho pepper grown in Essex.’

The seasonal menu is interestingly divided by what ingredients are available to the bartenders. The “lean season” ran from December to March; the current “plethora season” lasts till August, while September to November is “prep season”. A fourth low- and no-alcohol menu, “dry season”, is not only for January, but year-round.

Don’t expect to see the back bar laden with every cult Japanese whisky under the rising sun. The shelves are largely filled with unmarked bottles of mystery liquids – Nipperkin’s own distillates (for example, black tea or mushroom); cordials, shrubs and liqueurs; and branded spirits enhanced by fat-washing or steeping with an extra ingredient. The team doesn’t seem to have met a liquid it didn’t want to alter.

If you can persuade the team to go off-season (and the racks of bottles suggest some ingredients are there year-round), or can wait till December, Meech’s Quince and Beeswax cocktail is a prime example of what Nipperkin does. Bafas says, ‘The starting point for this cocktail was our head bartender Maxwell’s passion for organic beeswax. We created an amazing spirit, whisky washed with organic beeswax. And then we added a quince liqueur, some Exmoor raw wildflower honey and a touch of Capreolus quince eau de vie to finish it. Kind of an old fashioned, with very subtle aromatic characteristics.’

The whisky used is a mixture of Japanese and English (Suntory Hibiki Harmony and The Lakes’ The Whiskymaker’s Reserve No7). ‘What we say is that we’re in the business of blending, not the business of creating. Even if a brand is not mentioned on the menu, there is likely to be a blend of spirits in the cocktail.’

That blend approach is apparent in the highlight of the current menu – undoubtedly the Nipperkin take on a spicy marg, Sundried Tomatoes & Chillies, which contains Lost Explorer mezcal and tequila. But the star of the show is a tomato liqueur. Bafas explains how it is made: ‘We get our tomatoes from the Isle of Wight. They are delicious, but they have a very short season – about one and a half months when they’re at their best. We squeeze the water out of them, then take a 70 per cent spirit and dilute that with the tomato water. There are no bloody mary textures; it’s just a very clean, white spirit with intense tomato aroma. We also made a spirit with Scottish chillies, and have some sun-dried tomatoes infused to give an extra dimension to the drink. And half the glass is rimmed with sashimi spices mixed with salt.’

This is a cocktail with cult potential. However, loyalty to one drink is hard when there are intriguing combos to try such as Highland Park whisky, fennel absinthe and barley; Hendrick’s gin, pickled cucumber and wasabi distillate; or cristalino tequila, jasmine tea and mastiha. But the “plethora season” lasts till August, so there should be plenty of opportunities to explore.

nijulondon.com/nipperkin