How to Make It
Scrape the tomatoes and their juices from the packs into a food processor and pulse until coarsely chopped.
In a large pot, combine the clams and clam juice and bring to a boil. Cover and simmer over moderately low heat until the clams open, about 8 minutes. Remove from the heat. Using a slotted spoon, transfer the clams to a large bowl. Remove the clams from their shells, coarsely chop the meat and reserve. Strain and reserve the clam broth. Rinse out the pot.
In the same pot, heat the olive oil. Add the onion and cook over moderate heat until tender, about 5 minutes. Add the garlic and cook until fragrant, about 1 minute. Add the reserved clam broth, potatoes, chicken broth, thyme sprigs and bay leaf. Bring to a simmer, cover and cook over moderately low heat until the potatoes are tender, about 12 minutes. Add the chopped tomatoes to the pot, cover and simmer for 3 minutes. Discard the thyme sprigs and bay leaf. Stir in the chopped clams and season the chowder with salt and pepper. Ladle into bowls, sprinkle with the parsley and serve.