Heat the olive oil in a frying pan over a medium heat. Saute the onion, garlic and chopped mushrooms for 8 minutes until they soften and brown.
Cook the pasta according to the packet instructions in salted boiling water and then rinse through and drain.
Stir in the crème fraîche, simmer for 1-2 minutes, then stir in the onion, garlic and mushrooms, season with salt and freshly ground black pepper.
Serve in a wide pasta bowl.