LONDON — Just before lunch on a recent Monday, Jamie Oliver wrapped an apron around his dad bod and started mashing mint and broad beans with a mortar and pestle, which has long been his favorite kitchen tool.

That adorable mop of hair he had 20 years ago when he slid down a banister and splashed into popular food culture as the Naked Chef is cropped now. At 44, Mr. Oliver comes off more like a pleasant, world-weary high school teacher than the arrogant jokey bloke everyone wanted to hang around with back when he blew up food TV.

And are those bags under his blue eyes?

“Sorry, darling,” he said as he seasoned a fillet of Dover sole. “I’m a bit tired.”

The day started before 6 a.m. He dropped the kids at school, then made his way to the refurbished North London warehouse that serves as his headquarters. After feeding a reporter lunch, he had to meet top officials from Liverpool, Manchester, Birmingham and London who were coming by the office to hammer out a plan to halve childhood obesity rates by 2030.