1. Preheat the oven to 350°. Heat the fat or lard in an 8-inch skillet over high heat until a light haze forms over it, then reduce the heat to medium and add the onions. Cook them for 8 to 10 minutes, or until lightly colored.
2. Off the heat, stir in the paprika. Return the skillet to medium heat and add the peppers and tomatoes. Cover tightly and cook for 5 minutes, then stir in the wine.
3. Scrape half the vegetable mixture into a buttered 8-by-12-inch shallow baking dish, approximately 2 inches deep. Sprinkle the fish steaks generously with salt and a few grindings of pepper.
4. Arrange them in one layer in the baking dish, and cover with the rest of the mixture. Bake in the middle of the oven for 15 to 18 minutes, or until the fish is firm to the touch and flakes easily when prodded gently with a fork.
5. Arrange the fish steaks on a serving platter; cover them loosely with foil and keep them warm in a 200° oven while you make the sauce.
6. With a wire whisk, beat the flour into the sour cream in a small mixing bowl, then stir the mixture into the pan juices. Reduce the heat and simmer on top of the stove, stirring constantly, for 4 or 5 minutes, or until the sauce is thick and creamy. Mask the carp with the sauce.
