My maternal grandfather’s specialty was preparing fish, particularly his fish soup. On the Adriatic coast, where my family is from, it is known as brodetto, whereas on the Mediterranean side it is called cacciucco. The idea is the same: a delicate yet richly flavored assortment of fish and seafood in a tomato broth, born of fishermen’s need to utilize unsold fish. Its rich, sweet flavor came from stewing fish heads, then extracting the tasty morsels of flesh to add to the broth. In Essentials of Classic Italian Cooking, you’ll find my mother’s recipe, which faithfully reproduces my grandfather’s famous brodetto. It calls for cooking three or four fish heads in the base, then removing all the flesh with your hands and pureeing it back into the pot. When I am not in the mood to embark on such a project, or I am not able to get fish heads, I use the shells of the shrimp (or whichever crustacean you are using) to give it a richness of flavor instead. I cook them in the base only briefly, or my brodetto would end up tasting more like a bouillabaisse. My recipe also uses fish fillets, which is how most fish is sold in the States, rather than whole fish. To make it quicker and simpler, I don’t use squid, which require lengthy cooking to be tender, and because I like the lighter flavor this soup has without them. You can use any assortment of fish that does not include sole, because it is too bland, or mackerel and other blue fishes, because they are too strongly flavored. In addition to or instead of the shrimp, you can use rock shrimp or lobster. I use mussels but not clams, which I find are usually too tough. If you can get small, tender steamers, they would go very well here. Even though I’ve ended up changing my grandfather’s dish quite a bit, each bite still vividly reminds me of him.