Turn on the oven.
Scald the spinach in hot water for 2 minutes.
Drain thoroughly and chop finely.
Melt 50 g of butter on medium heat and then add the flour and simmer for 1 minute.
Take off the heat and add the milk, little by little, stirring until smooth.
Put the pot back on fire and stir continuously for 2-3 minutes.
Add the cream cheese, the chopped spinach, nutmeg and half of the grated Parmesan and mix until you get a homogenous sauce.
Heat the remaining butter in a different pan, and then add the mushrooms, the leeks and the garlic.
Sauté for 3-4 minutes. Add the tomatoes.
First, pour one quarter of the sauce on the bottom of a heat-resistant square pan (23x23 cm and 5 cm deep) then pour a third of the mushroom mixture, and layer of lasagna sheets on top.
Repeat the procedure twice more, ending with a layer of sauce on top.
Sprinkle the sliced almonds and then the Parmesan cheese on top.
Bake 25-30 minutes.
Serve the mushroom lasagna with a green salad.