It was the fall of 2023, and James Lowe, the London-based chef who’d made Lyle’s one of the UK’s best restaurants, realized he needed help. Despite 20 years of cooking experience, including stints in elite kitchens such as the Fat Duck and the River Cafe, the 45-year-old had never butchered a bluefin tuna. The UK had just awarded local licenses to catch the fish, though, so Lowe had ordered a 180-kilogram specimen from a favorite supplier in Cornwall.Carving up the pricey fish—especially a daunt...