Clean the spinach, wash thoroughly several times, drain. Peel onion and garlic, dice finely. Heat 10 g fat in a large pot, fry onion and garlic in it. Add the spinach, cover and let it collapse for 3-4 minutes.
Season with salt and pepper, drain. Cook the pasta in boiling salted water for about 8 minutes. Melt 40 g fat in a saucepan, sprinkle flour over it and sauté while stirring. Gradually stir in milk, Noilly Prat and 300 ml water.
Bring to the boil, stir in the stock and simmer for 5 minutes over a mild heat. Drain the noodles and let them drain. Season sauce with salt and pepper to taste. Wash fish, dab dry, sprinkle with lemon juice and season with salt and pepper.
Mix both cheeses. Grease the casserole dish (2 litres capacity). Spread about 1/4 of the béchamel on the bottom of the dish. Spread the pasta and spinach halves on top. Sprinkle with 1/4 of the cheese.
Add 1/4 of the sauce. Put the salmon on top. Layer the rest of the spinach, 1/4 cheese and the remaining noodles. Pour the rest of the sauce over the pasta and sprinkle with the rest of the cheese. Bake in the preheated oven (electric cooker: 200 °C/ convection oven: 175 °C/ gas: level 3) for 40-45 minutes.
If necessary, cover the last 10 minutes of the baking time. Serve garnished with basil.