Sauté the onion and garlic until they are well cooked.
Add the tentacles and the previously chopped fins and cook for about 20 minutes until the liquid released by the squid has been absorbed. Season the mixture.
After letting it cool, stuff the squid with the mixture. Do not overfill them, as they may burst due to shrinking. Secure with a toothpick and sauté in hot oil, reserving the juice they release.
In the same pan where the squid were sautéed, gently fry the onions and green pepper in olive oil.
Once they have softened, add the white wine, reduce, and add the tomato sauce. Add the fish stock and let it cook. Add the squid ink, cook for another 15 minutes, blend, and strain through a fine sieve.
Place the stuffed squid (after removing the toothpicks) into the sauce along with the juice they released while sautéing, and cook them over low heat until tender.