1. Smash half the pine nuts into a paste, then put them into a big heatproof bowl with remaining whole pine nuts, lemon zest and juice, chopped parsley, and olive oil. Stir, then add the Parmesan and pecorino.
Tip: The sauce should be reasonably thick—think of it as a dressing. Taste it, so you can balance the flavors and make sure it's quite zingy; as the sauce heats and cheese melts, the lemony flavor will calm down.
2. Put a large pot of salted water on to boil. Sit sauce bowl on top while water heats up—this will take the chill out. When water starts to boil, remove bowl and add pasta to pot. Cook pasta according to package instructions; drain, reserving a little cooking water. Toss pasta with sauce and reserved cooking water (try 1/2 cup) to loosen it. The heat from the pasta will melt the cheese, allowing the lovely sauce to coat it.
Tip: If you find the sauce too thick, add a little more water; it should be incredibly silky, fresh, and fragrant. Have one last taste to balance the flavors. Add some Parmesan and a sprinkle of parsley; enjoy immediately.