Never use just-picked basil for this; let the fresh leaves rest for one day to lose some of their moisture. The proportions for this sauce are not definitive, as the pungency of the basil varies. Small leaves are stronger in flavor and the taste is influenced by where it was grown. So test to see what your basil is like and adjust the amounts of the other ingredients accordingly.
You can keep this sauce, covered with a little olive oil in a jar in the refrigerator, for months. You can also make a pistou base (using basil, parsley, and a little oil) without completing the sauce and freeze it flat in a tight plastic bag; when you need it you can break some off and add the garlic and cheese.
Put a little of the basil, parsley, salt, pepper, garlic, and cheese in the mortar. Pound to a smooth paste and slowly pour in the olive oil (do a little at a time to make the pounding easier—it will take about 15 minutes to make it all into paste). If the consistency is too thick, you may add more olive oil.
Place a third of all the ingredients except the cheese in the blender and blend at high speed. Stop and scrape down the sides now and then. When the purée is smooth, put it in a bowl or refrigerator jar and purée the rest in two more batches. Add the cheese (this must be freshly grated in order to give the proper texture to the sauce, which becomes too smooth when made in the blender).
© 1990 Mireille Johnston estate. All rights reserved.