Cook the spaghetti in a generous amount of boiling salted water, then drain thoroughly and return to the saucepan.
Meanwhile, beat the lemon juice with the olive oil, then stir in the Parmesan until thick and creamy. The Parmesan will melt into the mixture. Season, and add more or less lemon juice to taste.
Add the sauce to the spaghetti, and shake the pan so that each strand is