In a low and wide casserole, sauté the onion and garlic in the olive oil over a gentle flame.until the onion is soft and translucent.

Dissolve the tomato paste in the vinegar and water add the mixture to the casserole. Raise the heat a bit and bring to a simmer. Season generously with salt and pepper.

Add the cephalopods and continue simmering for about 10-15 minutes. If you have some fish heads, add them also and then remove them before adding the next batch of fish.

Lay the fish in the casserole one piece at a time, starting with the largest and firmest varieties (such as monkfish and dogfish) then small whole fish, if using, and finally smaller and tenderer fillets. Partially cover and continue simmering until all the fish are cooked through and tender. (Simmer time can vary from as little as 10 minutes for fish fillets to as long as 25-30 minutes for whole fish.)

Finally, arrange the crustaceans over the fish and simmer until they have cooked through and turned pink, usually about 3-5 minutes.

Adjust the flame as needed to maintain a constant, gentle simmer throughout the above steps. If the broth reduces too much at any point, just add more water so the seafood remains about half covered. Do not stir once you've added the fish. If need be, gently shake the casserole.

Serve hot, with lots of crusty bread, grilled or toasted, on the side.