Trim the spring onions, removing the green part, the roots and the outer sheath, and cut into slices. Sauté them in a saucepan over low heat in 2 tbsp oil for 25-30 minutes, until they begin to break apart; if necessary, add a few tablespoons of water if they become too dry. Remove from the heat and blend with a generous grating of nutmeg.
Slice the calamari into thin strips and chop some basil leaves.
Prepare the anchovy-infused butter: place the oil-packed anchovies in a saucepan, mash them with a fork, and cook over low heat for 2 minutes. Add the butter, melting it over low heat. Remove from the heat and add 5 chopped basil leaves.
Cook the spaghetti in a large pot of boiling salted water. Drain 2 minutes prior to the indicated cooking time on the package.
Sauté the squid in a pan with 2 tbsp of the oil, 1 unpeeled garlic clove, and a pinch of salt for 2 minutes. Add the spring onion cream and a ladleful of the pasta cooking water. Drain the spaghetti and add to the pan along with the flavoured butter, and chopped basil. Stir well and cook for 2-3 more minutes until the spaghetti is al dente, then serve.