How to Make It
In a large flameproof casserole, heat the olive oil until shimmering. Add the garlic and cook over moderate heat, stirring, until golden, about 2 minutes. Add the mussels, cockles and wine. Cook over high heat, stirring, until some of the shells are open and the liquid has reduced by half, about 3 minutes. Add the tomato puree, tomato paste, crushed red pepper and a pinch each of salt and pepper; bring to a boil. Cook over high heat until the sauce thickens slightly, about 5 minutes. Stir in the squid, return the sauce to a boil and cook just until the squid is firm and opaque, about 30 seconds. Add the cream, reduce the heat to moderate and simmer for 1 minute. Season with salt and pepper.
Using a slotted spoon, transfer the seafood to a platter. Boil the sauce until reduced by half, about 10 minutes.
Meanwhile, cook the spaghetti in a large pot of boiling salted water until al dente; drain. Stir the spaghetti into the sauce and cook over moderate heat for 1 minute. Return the seafood to the pasta and toss well. Transfer the spaghetti to plates, garnish with the basil and serve.