Cook the spaghetti in a saucepan with salted water for 8-10 minutes, or according to the package instructions, until they are al dente. Then drain, drain and transfer to a bowl.
Pour the butter, parsley and half of the parmesan over the spaghetti and carefully fold in with two forks until the butter and cheese have melted and the parsley is well distributed.
Arrange the spaghetti in preheated bowls and sprinkle with the rest of the parmesan. Serve immediately with fresh, crusty bread.