Cook the spaghetti according to the package instructions, until al dente. Drain the water and add the olive oil and mix through.Whilst the spaghetti is cooking, heat the butter in a medium-sized frying pan and add the garlic and mushrooms - fry until golden brown. You may need to cook half the mushrooms at a time if your pan is not big enough - you don't want too many mushrooms in the pan at one time otherwise they will create too much liquid.Once the mushrooms are cooked, add the spaghetti to the pan and toss to mix with the butter, mushrooms and garlic.Add the parmesan, cream and basil as well as a generous sprinkling of salt freshly ground black pepper. Mix through