1. Sauté the previously chopped onion and garlic in olive oil.
2. Add the fish, cut into pieces, and cook for about ten minutes. Add the fresh cream and parsley. Season with salt and pepper, and mix well.
3. Preparation of the béchamel sauce:
Melt the butter, then add the flour. Mix well to obtain a roux. Gradually add the milk. Stir constantly until the mixture thickens and coats the spoon. Season with salt, pepper, and sprinkle with nutmeg.
4. Spread one third of the béchamel sauce on the bottom of the dish, cover with lasagna sheets, then add a layer of the fish mixture and béchamel sauce. Repeat this process until all the ingredients are used, finishing with a layer of béchamel sauce and cheese.
5. Bake for 25 minutes at 200 °C.