Bring a pot of salted water to a boil and cook the spaghetti until just tender, about 8 - 10 minutes. Put the butter, oil, and garlic in a small saucepan and cook over medium heat until the butter is melted and the mixture is hot. Remove from the heat and stir in the parsley. Drain the spaghetti, leaving about 1/3 cup of the pasta water in the pot. Return the spaghetti to the pot, toss with the butter mixture, and add salt. Serve hot, topped with the Parmesan cheese.