Rinse the fish under running cold water, pat dry, drizzle with lemon juice, let stand for about 15 minutes.
Peel and quarter the onions and cut into strips. Cut the bacon into cubes, heat the butter. Fry the bacon cubes in it, add the onion strips and sauté well. Season with sweet salt, pepper and paprika and let simmer in a closed saucepan for about 5 minutes.
Stir in the creme fraiche, season with salt, pepper and paprika to taste. Pat the fish fillets dry. Sprinkle with salt, pepper and paprika, place on the onion vegetables, cook in a closed saucepan for 7-9 minutes. Turn the fish fillets about halfway through the cooking time.