1. Preheat the oven to 400°F.

2. Prepare the bechamel sauce. In a saucepan, melt 50 g of butter. Add the flour and cook for 1 minute, stirring constantly without browning.

3. Remove from the heat and pour in the cold milk and vegetable broth cube all at once. Mix with a whisk.

4. Return to the heat and cook, stirring, until boiling. Season with salt, pepper, and nutmeg. Set aside.

5. Blanch the tomatoes in boiling water for 1 minute, then peel and seed them. Finely chop the tomatoes.

6. Set aside the most beautiful mushroom and cut the rest into cubes.

7. Sauté the chopped onion in extra virgin olive oil, then add the garlic and mushroom cubes. Cook, stirring occasionally, for 5 minutes over moderate heat; add the tomatoes. Season with salt and pepper. Continue cooking for 5 minutes.

8. Butter a baking dish and cover the bottom with a little bechamel sauce.

9. Place 3 lasagna sheets on top and cover with bechamel sauce, followed by the mushroom mixture. Sprinkle with raclette cheese cubes and cover with pasta.

10. Continue to fill the dish by alternating the different layers, ending with the bechamel sauce.

11. Finely chop the reserved mushroom and cover the dish. Sprinkle with grated parmesan.

12. Bake for 20 minutes, then turn off the oven and let it rest for 10 minutes before serving.