Cook the Spaghetti:
In a large pot of salted boiling water, add the spaghetti. Cook according to package instructions until al dente (usually around 8-10 minutes).
Reserve a cup of the pasta water, then drain the spaghetti in a colander and set aside.
Prepare the Sauce:
In a frying pan, heat the olive oil over medium heat.
Add the chopped onion and minced garlic. Sauté until the onion becomes translucent, about 3-4 minutes.
Add the Squid:
Stir in the squid rings and cook for about 3-4 minutes until they turn opaque. Be careful not to overcook, as squid can become rubbery.
Incorporate Cuttlefish Ink:
Add the cuttlefish ink to the pan. Mix well until the squid is fully coated. The ink will give the dish its signature black color.
Pour in the fish or vegetable broth. Bring the mixture to a gentle simmer and let it cook for about 5 minutes.
Combine with Spaghetti:
Add the drained spaghetti to the sauce. Toss gently to combine. If the mixture is too dry, add a little reserved pasta water to reach your desired consistency.
Season with salt, pepper, and optional chili flakes to taste.
Garnish and Serve:
Plate the spaghetti, garnishing with freshly chopped parsley.
Serve immediately while hot.