When done well, this age-old combination can be exactly what you want. Here, the cooking is as easy as the eating: While you get the soup started in a pot with a can of tomatoes and little more than onion and butter (in the style of Marcella Hazan’s famous tomato sauce), you assemble and pan-fry the sandwiches. The particular joy of these lies in their soft, quiet flavors: A thin layer of mayonnaise spread on the inside of the bread heats with the mozzarella, a mild cheese that lets you taste the bread and butter as they are. With a filling this rich and gooey, you want a delicate sweet enriched loaf like brioche or milk bread.