How to Make It
In a large bowl, soak the salt cod in plenty of fresh water in the refrigerator for 36 hours; change the water at least 5 times. Drain. Cut the cod crosswise into 1/4-inch strips.
In a medium saucepan, warm 3 tablespoons of the olive oil over moderate heat. Add the salt cod and cook, stirring gently, to heat through, about 3 minutes. Stir in 1 tablespoon of the flour until incorporated. Gradually mix in the milk. Reduce the heat to low and simmer, stirring often, until the mixture has thickened, about 25 minutes. Cool to room temperature.
Keeping the roasted peppers intact, remove any seeds and carefully stuff each pepper with a heaping tablespoon of the cod mixture.
In a large nonreactive skillet, warm the remaining 1 1/2 tablespoons olive oil over moderately low heat. Add the onion, carrot, parsley sprig and garlic and cook, stirring occasionally, until the onion is soft, about 12 minutes. Blend in the remaining 1/2 tablespoon flour and then stir in 1 cup of water. Bring to a boil, cover and cook for 10 minutes to blend the flavors. Uncover, stir in the sherry and simmer for 3 minutes. Transfer the mixture to a food processor and puree until completely smooth. Pour the sauce back into the skillet. Season with kosher salt.
Carefully place the stuffed peppers in the sauce. Cover and simmer gently over low heat until the peppers are heated through, about 3 minutes. Transfer the peppers to serving plates and spoon the sauce around them. Sprinkle the chopped parsley on top and serve at once.