In a pot large enough to contain all your seafood comfortably, sauté the onion, carrot, celery, parsley, garlic and red pepper flakes in abundant olive oil over low heart until quite soft. Add a pinch of salt as you sauté, taking care not to let anything brown.
Add the tomatoes to the pot and let them reduce for a few minutes into a saucy consistency.
Lay on the fish and other seafood, then add enough water to cover the seafood, along with the bay leaf and saffron if using. Simmer, uncovered, for a good 20-30 minutes, until the seafood is cooked through and broth is very flavorful. Taste and adjust for salt.
Remove the fish and other seafood from the pot. Using a paring or boning knife, remove the skin and filet the fish. Cut the filets, if need be, into serving-size pieces. Place the fish filets and shellfish in a bowl and cover to keep warm. Discard the fish heads, skin and bones.
Pour the remaining broth through a fine sieve, pressing out the liquid from the solids, and return it to the pot, along with the seafood.