1. Preheat the oven to 400°F (200°C). Heat the oil in a flameproof casserole over medium-high heat. Add the fish, skin side down, and cook, for 1 minute, or until the skin is crisp. Turn and cook for 1 minute longer. Using a slotted spatula, transfer to a plate.

2. Add the onions and garlic to the casserole and reduce the heat to medium. Cook, stirring frequently, for about 4 minutes, until softened. Add the stock, tomatoes, wine, and tomato paste and bring to a simmer. Simmer, stirring often, for 10–12 minutes.

3. Place the fish in the sauce and bake for 5-10 minutes, or until barely opaque. Transfer the fish to a platter and tent with aluminum foil to keep warm.

4. Cook the sauce over medium-high heat about 3 minutes, until reduced and thickened. Stir in half the parsley and season to taste with salt and pepper. Divide the sauce among 4 dinner plates and place a piece of fish on top. Serve at once, sprinkled with the remaining parsley.

Variation:

Halibut in Tomato Sauce: Replace the cod with the same quantity of halibut and use basil and dried chile flakes, instead of the parsley.