Josephine is a Lyonnaise bistro on the Fulham Road from Claude Bosi. It is named for Bosi’s grandmother and is that rare, magical thing: a perfect restaurant. Bosi runs Bibendum (two Michelin stars, and in Michelin House) and Brooklands at the top of the appalling Peninsula hotel (two Michelin stars). He opens a second Josephine this month in Marylebone, which needs it since the Chiltern Firehouse, always a restaurant that felt like Icarus with a kitchen, burnt down to rubble. I haven’t eaten in Brooklands – I wish the Peninsula were an island, so that it could float to Victoria and then away, being an oligarchic monstrosity. But my instinct is: this is the good stuff.

When you feel love in a restaurant, you are in the right place, even in Chelsea

The exterior is painted navy blue: it has been washed by a maniac. It is smart even for Chelsea, which is always absurd – it’s the awful closeness to Fulham that corrupts it. I am 40 minutes early and arrive during a rainstorm, and I know I am in a perfect restaurant within seconds, as you do, because the diner’s instincts for security are the same as a child’s. I am settled immediately with the prelude: real French bread, (unsalted) butter, lumps of deep-fried pig fat (grattons Lyonnais) in a terra-cotta bowl, which taste better than they sound, being pork scratchings.

The interior is as perfectly wrought as a stage, which it is. There is a ruby red curtain at the entrance to repel the street, dark wood walls, a pale mosaic floor, fine lighting, posters for the long-dead of Lyon. I think Bosi loved his grandmother very much, and when you feel love in a restaurant you are in the right place, even in Chelsea. This is an idealised bistro, but all great chefs are dreamers.

Still, nothing is perfect. By nothing I mean common people. The tables are tightly packed and to get up for the loo I have to push ours out. As I try to push it back, the woman at the next table – dining with a recently separated man (a diarist’s instincts cannot die) – moves into my spot and starts wiping her coat. I cannot push the table back so I just stand and stare at her, a portrait of invisibility. As the manager catches my eye in sympathy – all managers of perfect restaurants have variations on Sauron’s eye – the recently separated man turns to me and hands me his empty wine glass. When he learns I am not a waiter, he apologises and forgives himself instantly, because he is a handsome man and forgiveness has never been denied him. Personally I think coat-wiping woman is making a mistake, but you can’t save everyone. And this is why I never come to Chelsea.

Still, you should come to Chelsea for Josephine, because the staff are kind – the teenage waiter laughed when he saw me gawping because he was eating Birds Eye fish fingers and chips for his lunch – and the food is wondrous. My companion says Josephine thrives here because it is near the Royal Marsden Hospital, and I think he is right.

We eat soupe à l’oignon, which I can never get enough of; ris de veau aux morilles; a gratin dauphinois so good I look at its picture afterwards, like a dog who licks a smell; choux à la crème as big as a tennis ball; baba au vieux rhum, which delights my companion because it reminds him of the Disco Age without the heartbreak; plateau de fromage from a board delivered to the table, from which you help yourself; too many scratchings and too much French bread. We stagger out at teatime. We would have stayed longer.