Soak the dried cod in cold water, changing the water every 4 hours, for 3 days. (Alternatively, you can buy pre-soaked dried cod.)

Remove some of the skin, the backbone, and all the bones from the cod. Cut it into evenly sized square pieces.

Finely slice the onions and sauté them in a pan with 1/2 cup (about 120 ml) of olive oil. Add the anchovies and cook for a few more minutes. Remove from heat and stir in the chopped parsley.

Spread a few spoonfuls of the onion mixture on the bottom of a Dutch oven or heavy pot. Dredge the cod pieces in flour and arrange them side by side in the pot. Top the fish with the remaining onion mixture, salt, pepper, milk, olive oil, and Parmesan cheese.

Cook over very low heat (preferably with a heat diffuser) for 6 hours, stirring occasionally to prevent the cod from sticking to the pot.