Heat some water in a pan and, when it comes to the boil, add the pistachios. Cook for five minutes, strain (save 70 ml of the water for later) and leave to cool. Peel while still warm (the skin should come off easily).
In a blender, add the pistachios, Parmesan cheese, garlic, grated zest of half a lemon and the basil. Finally, add the 70 ml of water put by earlier. Slowly blend and gradually add the extra-virgin olive oil. When you obtain a smooth mixture, add salt and pepper and blend a little more.
This tasty sauce will keep in the fridge for about three days; you can also freeze it. It works wonders with farfalle, which have the perfect shape!