Special equipment: Cataplana pot (15-inches across), or a large heavy Dutch oven type of kettle
Meanwhile, prepare the sauce: Cook the onions, garlic, and green peppers in the oil in a large heavy skillet over moderate heat for 8 to 10 minutes, or until limp and golden. Add the bay leaf, tomatoes, and their juice. Break up any large clumps of tomatoes, bring mixture to a simmer, cover and cook slowly for 30 minutes; add the tomato sauce, prosciutto, smoked ham, and chourico; cover, and cook 30 minutes longer. The sauce can be made as much as 2 days ahead of time but do not buy the clams until the day you plan to serve the cataplana. The sauce should be covered and refrigerated until you are ready to proceed.
To assemble the cataplana: Spoon 1/2 the tomato mixture into the bottom of a very large cataplana pot, and bring to a simmer over moderate heat. Adjust the heat so that the mixture barely boils, arrange the clams on top, spoon in the remaining tomato sauce and wine, cover tightly, cook 10 minutes over moderately low heat, do not lift cover. Open the cataplana or kettle, scatter the parsley evenly on top, and then toss the clams lightly. If clams have not opened, cover and cook slowly for 5 to 10 minutes longer or until the clams open. Discard any that do not.
Carry the cataplana or kettle to the table, take off lid, and ladle into large soup plates. Cook's note: Types of small clams to use are West Coast butter clams or small Littleneck clams. Also, be sure to put out a large bowl for empty clamshells.
Types of small clams to use are West Coast butter clams or small Littleneck clams. Also, be sure to put out a large bowl for empty clamshells.