Cut the mushrooms into thin slices and leeks into thin circles. Add oil to a pan or wok. Toss in the sliced mushrooms and add salt and pepper to taste. Once the mushrooms have slightly sauteed, add the leeks, parsley and sour cream. While slowly stirring, cook for about 2 minutes. Finally, add the basil.
Cook the spaghetti in slightly salted water and, once ready, mix with the prepared sauce. Serve warm.