Wash the mussels in cold water. Place a large pot with 3-4 l salt water on top and cook the spaghetti in it according to the instructions on the packet.
Peel and chop the white onion. Clean the mushrooms and chop roughly. Wash and halve the cherry tomatoes. Wash the parsley. Pluck leaves and chop stalks and leaves separately. Clean and wash spring onion, also chop finely. In a large frying pan, sauté the white onion in some olive oil. Add the mushrooms, cherry tomatoes and parsley stalks, cover the pan and let it simmer for 5-10 minutes at medium heat.
Now add the mussels to the pan, fold in the spring onion and parsley leaves. Deglaze with white wine and cream, bring to the boil and cook for about 4 minutes. Season to taste with salt and pepper, mix with the ready cooked spaghetti and toss well.