No French dish is as steeped in history, myth and religion as cassoulet. Natives of southwestern France's Languedoc region link their very cultural identity to the archetypical peasant dish, a rich, earthy casserole of beans, meat and herbs. Cassoulet is said to date back to the 14th century siege of Castelnaudary during the Hundred Years' War, when citizens created a communal dish so hearty their revivified soldiers sent the invaders packing. But since then several cities have laid claim to the true recipe. In a conciliatory gesture, chef Prosper Montagné decreed in 1929 that "God the father is the cassoulet of...