1. Pinch off the basil leaves from the bunch. Don't wash them (they mustn't be wet).
2. Put them in a mortar along with the pine nuts, the garlic and the salt and work these ingredients over with a pestle until they're completely crushed and well blended together.
3. Put this "paste" into a larger bowl. Alternately add small amounts of olive oil and parmesan cheese, while stirring constantly until you have the desired consistency (creamy).