OPTIONAL: Prepare an ice water bath in a large bowl, and bring a large pot of water to a boil. Put the basil in a large sieve and plunge it into the boiling water. Immediately immerse all the basil and stir so that it blanches evenly. Blanch for about 15 seconds. Remove, shake off the excess water, then plunge the basil into the ice water bath and stir again so it cools as fast as possible. Drain well. Squeeze the water out of the basil with your hands until very dry.
Roughly chop the basil and put in a blender. Add the olive oil, pine nuts, garlic, vitamin C if using and salt and pepper to taste. Blend for at least 30 seconds. In this way, the green of the basil will thoroughly color the oil. Add the cheese and pulse to combine. The pesto will keep several days in a tightly sealed container in the refrigerator. Makes about 3/4 cup.
Cook's Notes: If your pesto typically turns army green shortly after you make it, you'll appreciate the beauty of this version. I blanch the basil briefly to set the color, and I add a pinch of powdered ascorbic acid (vitamin C), which keeps the pesto from oxidizing.
I use pure olive oil for pesto so the clear flavor of the herb dominates. If you want to freeze the pesto, omit the nuts and cheese.