Jeez, not another Ruth Rogers pasta recipe. This one is absurdly simple and relies on the quality of the ingredients and your instincts in combining them at the right time and at the right temperature.
Slowly stir the zest and juice of two lemons into 1/2 lb freshly grated reggiano until you have a thick sauce. Add enough olive oil to make a thick, creamy consistency. Add salt and pepper and keep tasting, adding more oil if the sauce is too astringent. Cook 2/3 lb spaghetti in salted boiling water until al dente, and then drain, reserving 2 tbs of the cooking water (very important). Return to the warm pan, stir in the sauce making sure to coat every strand, and then add the reserved cooking water, loosening the mixture and completing the marriage of sauce and pasta. Add 4 tbs roughly chopped basil, and serve immediately with extra reggiano.
Good, real reggiano and excellent, completely fresh olive oil and basil are essential.