Cook the pasta half cooked, drain, rinse and place in a flat dish. Clean the mushrooms, cut into slices and mix with the pasta. Depending on your taste, add a few pellets of the frozen spinach to the mold.
Dice the onion, finely dice the garlic and sauté in a little oil, then add the cream and milk. Simmer a little and dissolve the processed cheese in the cream-milk mixture. Season well with salt and pepper. Pour the liquid over the pasta, mix in some grated cheese, and distribute the rest on top.
In the oven at 160 degrees for 30-45 minutes, or until the cheese is golden brown.