In a blender container or food processor bowl combine fresh basil leaves; parsley sprigs; grated Parmesan or Romano cheese; pine nuts, walnuts, or almonds; garlic; and salt. Cover and blend or process with several on-off turns until a paste forms, stopping the machine several times and scraping the sides.
With the machine running, gradually add olive oil or cooking oil and blend or process to the consistency of soft butter. Divide into 3 portions (about 1/4 cup each) and place in small airtight containers. Refrigerate for 1 or 2 days or freeze up to 1 month.
To serve, thaw 1 portion pesto, if frozen. Bring to room temperature. Makes twelve 1-tablespoon servings.