If using dried salt-cured fish, begin by soaking the Stockfish (dried unsalted cod) in cold water for 24–48 hours in the refrigerator, changing the water several times until the flesh is pliable and dessalted; then remove any bones and skin and cut into 2–3 cm strips.
Thinly slice the Onion and finely chop the Salted anchovy fillets.
In a wide, heavy pan, warm the Extra-virgin olive oil over low-medium heat and gently sweat the sliced onion until translucent and very soft, about 20–30 minutes—do not let it brown.
Add the chopped anchovies to the onions and stir until they dissolve into the mixture, then dust in the Plain flour and cook for a minute to remove the raw taste, stirring constantly.
Nestle the pieces of stockfish into the pan, pour in enough Whole milk to come halfway up the fish, bring to a gentle simmer, cover partially and cook very slowly for 1½–2 hours, stirring occasionally and adding more milk or a splash of water if it becomes too dry; the sauce should become creamy and the fish should flake easily.
A few minutes before the end of cooking, stir in most of the grated Grana Padano and chopped Parsley; season carefully with Fine salt and freshly ground Black pepper to taste (keep in mind the anchovies add saltiness).
Prepare the Soft polenta according to package or preferred method so it’s warm and spoonable when the fish is ready.
To serve, spoon a generous bed of polenta onto plates and top with the baccalà, finishing with the remaining Grana Padano and a sprinkle of parsley. Enjoy warm.
