Bill Yosses, the White House pastry chef, offers a rare insider’s view of the operation and says there is no contradiction in being a dessert maker for such an avowedly health-conscious first family. The president calls him “The Crustmaster.” Yosses, who co-authored “Desserts for Dummies” and another cookbook, had been executive pastry chef at a series of top restaurants before he arrived at the White House in January 2007, two years ahead of the Obamas.