The dish is named after its traditional cooking vessel, the cassole, a deep, round, earthenware pot with slanting sides.
The region once known as the province of Languedoc is the traditional homeland of cassoulet, especially the towns of Toulouse, Carcassonne, and Castelnaudary, the town which claims to be where the dish originated. All are made with white beans (haricots blancs or lingots),[a] duck or goose confit, sausages, and additional meat. In the cassoulet of Toulouse, the meats are pork and mutton, the latter frequently a cold roast shoulder. The Carcassonne version is similar but doubles the portion of mutton and sometimes replaces the duck with partridge. The cassoulet of Castelnaudary uses a duck confit instead of mutton.
In France, cassoulets of varying price and quality are also sold in cans and jars in supermarkets, grocery stores and charcuteries. The cheapest ones contain only beans, tomato sauce, sausages, and bacon. More expensive versions are likely to be cooked with goose fat and to include Toulouse sausages, lamb, goose, or duck confit.
Haute cuisine versions require mixing pre-cooked roasted meats with beans that have been simmered separately with aromatic vegetables, but this runs counter to cassoulet's peasant origins. In the process of preparing the dish it is traditional to deglaze the pot from the previous cassoulet in order to give a base for the next one. This has led to stories, such as the one given by Elizabeth David, citing Anatole France, of a single original cassoulet being extended for years or even decades.
In American restaurants, the term "cassoulet" is often applied to any hearty bean-based casserole, with innovations such as salmon cassoulet.
Many culinary traditions have similar techniques for slow cooking beans in a covered vessel. Examples include feijoada, fabada asturiana, pasulj, tavče gravče, and baked beans. The Hungarian-Jewish sólet and Eastern European cholent are similar bean dishes, and are also frequently cooked in combination with smoked poultry, especially goose leg, but a documented relationship has not so far been identified.