Cholera is a Valais pie from the upper Rhône valley, especially the Goms district, filled with layers of potato, leek, apple, pear and mountain cheese under a pastry lid. One story ties the name to the 1830s cholera outbreak, when people stayed home and baked whatever was in the cellar; another to the old Valais word for a coal stove, chola. It is eaten warm or cold, as a Sunday lunch, picnic food or a slice with a green salad, and the sweet fruit against salty cheese and soft leek is the whole point. Some Valais cooks add bacon; this vegetarian version doesn't need it. Use cheese made with vegetarian rennet. Chef's tip: slice the potatoes, apples and pear thinly and evenly (3 mm) so everything cooks through in the time the pastry takes to brown.