For the pasta chiara, blanch the tomatoes and peel off the skin, cut into cubes. Dice the onion and garlic. Cook the pasta in plenty of salted water until al dente. Save a little of the cooking water.
Sauté onion in olive oil (leave rather light), add garlic and pour in tomatoes. Simmer for about 1 hour (add a little pasta cooking water if necessary), salt and pepper.
Clean and slice the mushrooms and sauté them with the second onion in olive oil (should also remain rather light).
Add the mushrooms to the tomatoes and mix with the pasta. Sprinkle with freshly grated Parmesan cheese.