Cook the spaghetti in a large pan of lightly salted boiling water for 8 mins or until al dente.
Meanwhile, heat a large pan over medium heat. Add the extra virgin olive oil, followed by the finely chopped onion, mushrooms and garlic. Cook over medium-low heat for 5 minutes, then add the spinach leaves and cover with a lid. Stir occasionally until the spinach leaves are tender, and season with salt and pepper. Discard the garlic and remove the pan from the heat.
Drain well the spaghetti, reserving a ladleful of the pasta water.
Transfer the spaghetti into the pan with the other ingredients. Stir in the crème fraîche, the cheese and the reserved cooking water if necessary.
Heat through for a minute, mixing well all the ingredients. Season to taste with black pepper and serve immediately.
