Cook the pasta in a large saucepan of salted boiling water according to the packet instructions until al dente.
Meanwhile, put the basil, pine nuts and garlic in a food processor and process until well blended. Transfer to a bowl and stir in the Parmesan and oil. Season with salt and pepper.
Drain the pasta, reserving a ladleful of the cooking water, and return to the pan. Stir in the pesto, adding enough of the reserved pasta cooking water to loosen the mixture. Serve immediately with a scattering of grated Parmesan and garnished with basil leaves.