In a large enameled cast-iron casserole, heat the extra-virgin olive oil until shimmering. Add the smashed garlic and cook over moderately high heat until fragrant, about 30 seconds. Add the pureed tomatoes, the clam juice, thyme, basil and sugar. Season with salt and pepper and bring to a boil. Cook over moderately low heat until it is reduced by one-third, about 45 minutes. Add the squid and cook over low heat until very tender, about 45 minutes longer.