Tonight, Nigella Lawson will be guest of honour as London's Jewish Museum opens its new grey metal doors in Camden. Inside the extended building, the (almost) fabulous baker boys – not to mention Yiddish karaoke – are waiting for a new audience. Bakers and karaoke are not just trivial factoids. They're typically lively subjects in a reborn museum determined to illuminate the values, history and achievements of Jewish life in a way that does not allow the potentially consuming shadows of the Holocaust to dominate.
Frank Gehry, speaking of another architect, once wondered aloud to me: "Why doesn't he ever do a joyful building?" London's Jewish Museum is on this side of life, and Gehry would surely admire it, even though it doesn't feature a giant carp, the fish whose form has had such a shamanic influence on his work.
The fish and the hand are, of course, key Jewish symbols. And it's easy to imagine the floury fingers of the Whitechapel baker boys holding up their wonderfully vivid trades union banner, now ensconced in a 4-metre wide vitrine. It reads: abolition of night work 8 hours day. Two flights of stairs up, in the £10m museum extension designed by architects Long & Kentish, are the J G & Sons baking tins, many of them used 70 years ago.
A little further along, in a small gallery dedicated to the London-born Holocaust survivor Leon Greenman, we encounter the pink-painted wooden truck he made for his two-year-old son, not knowing at the time that the boy and his wife had been killed almost immediately on arrival at Birkenau in 1943, in a snow-covered landscape starkly littered with abandoned suitcases.
The decision to portray British Jewry's experience of the Holocaust in this way makes it personal and singularly touching, in a way that the overwhelmingly dreadful number, six million, cannot. The rigour of this focus on a single survivor pervades the overall exhibition strategy: despite tripling the museum's size, lead architect M J Long, collaborating with museum director, Rickie Burman, has created a series of domestic-scale gallery spaces – low-ceilinged, quite narrow – that generate an intimate rather than portentous narrative.
There is nothing declamatory going on in these spaces; nor is this an exercise in the creation of metaphysically loaded space. Indeed, it's very clear that the museum is going to be enjoyed by younger visitors in particular. There are screens and interactives – including an Ask The Rabbi gizmo – but not too many. The historical evidence is mainly artifactual, as if to accentuate the physicalities of Jewish worship and history, and of living and doing. And contemporary eating and buying, naturally: there's a café and shop.
The new architecture is actually old architecture transformed by three basic interventions: a new entrance sequence; a beautifully designed staircase; and a skilled smoothing out of tricky level-changes between the volume of the original 1840s neo-Georgian terrace building facing Albert Road, Camden, and its connection to the now reinvented piano factory just behind it.
It's apt that the Ajello family made pianos for the King of Italy here in the 19th century, and that the front half of the Jewish Museum – its original cramped quarters – had been a prosthetics workshop until being taken over following the amalgamation of the London Museum of Jewish Life and the Jewish Museum in 1995. These buildings had been places where people made things with skill. And the work of hands – more often basic, rather than exquisite – is evident in most of the museum's exhibits.
There are some stunners in the 25,000-item collection, though: Micheal Issacharoff's ravishingly patterned 1933 silk and velvet barmitzvah robe is one of the first things visitors will see. It not only begins to signal the ethnic diversity of Jews – Issacharoff was from Samarkand in Central Asia – but will also be coveted by dedicated followers of fashion.
The museum design supports a mingling of the serious and the playfully humane: The Man Wot Knows How to Drive a Bargain, Rowlandson's satirical 1829 depiction of the fabulously wealthy N M Rothschild as an old clothes dealer; a small homage to the great war poet Isaac Rosenberg next to a display about the king of inter-war Jewish wedding photographers, Boris Bennett; and wooden hat-moulds recalling René Magritte's surreal art a few paces away from an open page from a 1912 edition of Jews' Free School Magazine, which reads: "19. This magic number represents our success at this year's examinations for Junior County Scholarships. Nothing like it has been achieved before, and everybody is elated at the distinction... "
The architecture takes a considerate back seat to these cultural montages. M J Long has allowed herself only one deliberate moment of drama, and it doesn't quite work. A segmented mirror above the stones of a 13th- century mikvah ritual bath, originally excavated in the City of London, is supposed to signal the mikvah's presence in the line-of-sight at the moment of entry into the first gallery. Alas, the shard-like mirrors are rather ungainly and optically confusing: even from a few steps away, one has no clear idea that there's a sunken bath beneath them.
But the rest of the architectural inventions have a properly unfussy gravitas. Long's palette of oak joinery and panelling, white walls, and grey-painted steel sits comfortably alongside the knobbly rivets and chunky steel beams of the original 19th-century piano factory structure, in the same battleship grey paint. This calm architectural treatment reconciles the past and the present practically – a significant word, implicit in virtually everything one learns here, beginning with William the Conqueror's decision to encourage the Jews of Rouen to emigrate to England in 1066 and stimulate English trade in new ways. Cromwell was equally practical in 1656, for the same reason, following the Jews' expulsion from England in 1290.
Cycles of Jewish cultural development and physical movement are made very evident, not just in the museum's range of exhibits, but in the way the narrative is set out in the meandering peristalsis of small spaces. Even the museum's six-sided worship room is bordered with alcoves so that particular facets of Jewish life – such as the celebration of the Sabbath at home – are presented with direct simplicity.
There has been no attempt to imbue this crucial room with leaden sanctity, and it's refreshing to learn that its magnificent 17th-century Italian ark might, under different circumstances, have triggered a feral glint in the collective gaze of an Antiques Roadshow audience. The ark was found and identified, by chance, in 1932 at Chillingham Castle in Northumberland, where it was being used as a steward's wardrobe.
Jewish Museum, London NW1 (020 7284 7384) reopens on 17 March