The Croque Monsieur is a classic French ham and cheese sandwich that first appeared on Paris café menus in 1910. The name comes from the French words 'croquer' (to crunch) and 'monsieur' (mister). Its defining characteristic is the use of Gruyère or Emmental cheese and a rich Béchamel sauce, which is often spread on top and grilled until bubbly. If a fried egg is placed on top of the sandwich, it becomes a 'Croque Madame'—the egg is said to resemble a woman's hat of the era. The sandwich gained literary fame when Marcel Proust mentioned it in his 1919 novel 'In the Shadow of Young Girls in Flower.'