Wash the basil, discard the stems, and dry throroughly. In a food processor or blender (I use a food processor), puree the basil with 1/4 cup of the olive oil, the pine nuts, garlic, and Parmesan until thick and homogenous. With the machine running, add the remaining olive oil in a thin stream to create a smooth paste.
Yield: 1 cup
This makes enough pesto for 1.5 pounds dried pasta, cooked.