A s we sit down to chat in his light and airy test kitchen, Yotam Ottolenghi offers a plate of freshly baked cheddar and pistachio biscuits, still warm from the oven. As you might expect, they are delicious. The initial strong cheesiness is quickly overtaken by a detonation of pistachio.

The biscuits have been popular in Ottolenghi’s delis since he opened his first 20 years ago. “A constant, right from the beginning. Then recently they started giving us trouble,” he says. He is smiling now because a week of hard work seems to have solved the problem. But it was, he says, “a crisis”.

Pistachios, like za’atar and preserved lemons, are ingredients that have become closely associated with Ottolenghi, the chef who has done more than

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