For the haddock with mushrooms, first preheat the oven to 220 °C and grease an ovenproof dish with butter.
Rinse the fish fillets and pat dry. Sprinkle with the juice of one lemon, season with salt and place in the mold.
Now dice the bacon and fry it in a frying pan. In the meantime, wash the mushrooms, quarter them and add them to the fish in the mold. Spread the bacon cubes evenly on top and pour white wine.
Put the pan in the oven on the middle shelf and cook the fish for 15-20 minutes. Then keep warm on a preheated plate.
Mix the roast stock with crème fraiche, season with onion salt, pepper and soy sauce and drizzle over the fish.
Arrange the haddock with mushrooms on plates and garnish with freshly chopped chives.