Step 1Remove the skin and cut the fish steaks into serving pieces. Blend the salt and lemon juice in a 13x9-inch glass baking dish,then beat in 6 tablespoons of the oil and half the pepper. Place the fish in the dish and baste with the marinade. Cover with wax paper and marinate 1 1/2 to 2 hours at room temperature, turning and basting the fish with the marinade several times. Drain the fish and dry it thoroughly on paper towels. Discard the marinade, which will be strong and fishy. Wash out the dish.
Step 2Cook the fish rapidly in a large skillet over high heat in 3 to 4 tablespoons of very hot olive oil, a minute or two each side, to brown lightly. Return the fish to the dish.
Step 3Heat the oven to 350 degrees. Cook the onions slowly in the skillet for 5 minutes, until tender but not browned. Stir in the tomato pulp, garlic, oregano, thyme, salt and remaining pepper. Cover and cook slowly for 5 minutes. Correct the seasoning and spread the tomato mixture over the fish.
Step 4Place a cover or aluminum foil over the baking dish and place in the lower third of the oven. Bake for 15 minutes. Pour in the wine and bake 30 minutes more, turning the oven down to 325 degrees as soon as the fish is simmering.
Step 5Remove the fish to a serving platter, scraping the sauce off the fish and back into the baking dish. Keep the fish warm for about 5 minutes while finishing the sauce.
Step 6Boil down the sauce in a skillet over high heat until it has reduced to about 2 cups. Stir in the tomato paste. Simmer for a moment and correct the seasoning.
Step 7Off heat, beat in the flour and butter paste, and bring again to a simmer for 1 minute. Stir in the chopped parsley, spoon the sauce over the fish and serve.