The foundation of this creamy casserole is a classic mornay sauce, a béchamel sauce to which cheese has been added—in this case, comté, a French cheese with a complex, nutty flavor that melts beautifully. With lots of freshly grated nutmeg to season it and a golden, crunchy breadcrumb topping, it’s a luscious, satisfying side dish for the Thanksgiving table. The dish comes from Thomas Keller’s Bouchon Bistro, in the Napa Valley, where the staff makes it as part of their annual Thanksgiving dinner for veterans and their families.