Yotam Ottolenghi collaborates with Ixta Belfrage from the Ottolenghi Test Kitchen on his latest cookbook, “ Flavor ,” which he describes as everything he’s learned about vegetables in the last five years. With vegetable-focused recipes, Belfrage uses her background in Mexico and Brazil to navigate Ottolenghi’s repertoire in a different direction. Together, they highlight common ingredients like onions, garlics, and leeks in unpredictable ways.