Tristram Stuart has 24 hours to produce a restaurant meal for 50 people—to plan a menu, gather food, then welcome guests to a venue in a city not his own. Complicating what sounds like a reality-show contest is a singular rule: Nearly all the ingredients must be sourced from farms and vendors intending to throw them out. After racing back to New York City from a New Jersey farm where he gleaned 75 pounds of…