The move completes a circle which took him to Australia, where his foodie passion became an obsession, and back again, in the decade since he started confounding room-mates at Birmingham University.
"Instead of baked beans on toast I was making stroganoff, or Jamie Oliver's seared yellowfin tuna with soy sauce," he confesses. "I put it down to a home where we enjoyed big Friday night dinners, big Sunday lunches and ate out a lot in restaurants.
"Perhaps that's why my parents, who are keen cooks, sent me to the Cordon Bleu - or perhaps it's because they have always been supportive."
Josh himself was less convinced he should abandon a conventional path, using his new cooking skills to put himself through a master's in business - and eat his way across Sydney. "I worked in a gourmet burger joint and spent everything I earned on restaurants.
"I loved the way their cooking was about the best ingredients and fusing influences from all over the world." Yet when he came home he went into a marketing job he had no heart for. After taking time out for yet more foodie explorations in South America, Katz finally wrote to five top London chefs asking if at 24 he was too old to start cooking.
"Only Gordon Ramsay gave me the brush-off; all the others sent back encouraging letters, and the Galvin brothers invited me to work in the kitchen of their Baker Street bistro for a week. At the end they offered me a job. I stayed 15 months."
Convinced that the only way for a nice Jewish boy to make a living from food was in catering, Katz spent a miserable year doing canapés ("making 400 of the same thing drove me crazy"). Surprisingly, his worst large-scale gig was Bruce Springsteen's European tour: "They had a very small budget.
"Springsteen demanded watermelon which had to be de-seeded, and I had to make a chicken soup absolutely nothing like the one my mother makes."
Finally, Katz got into his stride at Ottolenghi, loving the fusion of Mediterranean and Asian influences, and enjoying a happy time as sous-chef before bidding for his own kitchen at the Roundhouse.
Surprisingly, his wonderfully spicy shakshuka comes not from his Israeli former employer, Yotam Ottolenghi, but Israeli backpackers he met in Australia. "They were always cooking it up at our digs. But here in London I just call it baked eggs."
Other signature dishes include pumpkin risotto and mackerel with beetroot mousse and an apple wasabi slaw.
Katz often finds himself serving his father the radiologist, his mother the psychotherapist and the two brothers who followed more conventional paths, relieving him of his early compulsion to do the same. "And they all seem to be quite proud of what I've done here," he says, with a hint of surprise in his voice.
Josh Katz's Shakshuka
Serves four
Ingredients
● 2 tbsp olive oil
● 1 onion, peeled and finely chopped
● 2 garlic cloves, finely chopped
● 1 red pepper chopped
● 1 red chilli, finely chopped
● 2 tsp smoked paprika, smoked
● 1 tbsp. tomato puree
● 1 50g tin plum tomatoes
● 1 tsp chilli flakes
● Salt and pepper
● 8 eggs
● 2 tablespoons flat leaf parsley, chopped
● 4 tsp Greek yoghurt
● Paprika to garnish
Method
● Preheat oven to 180°C, then sweat onions and garlic in olive oil until softened.
● Add pepper and chilli and cook down for 5-7 minutes until pepper softens, stirring regularly.
● Add paprika and cook for 1 minute, then stir in the tomato puree and cook for 2 minutes.
● Add tomatoes and chilli flakes, bring to the boil, then simmer for 5-20 minutes, seasoning to taste.
● Transfer sauce to a wide frying pan able to accommodate 8 eggs, or divide between 2 pans.
● Bring sauce to simmer then crack eggs into a well.
● Cook for 1-2 minutes then transfer to oven for a further 5-7 minutes.
● The eggs are cooked when the white is set but the yolk remains runny.
● To serve, remove pan from the oven, sprinkle with parsley and dot with dollops of yoghurt. Scatter with a pinch of paprika and drizzle with olive oil.
● Serve with toasted or grilled sourdough bread.
