Fresh basil varies from week to week and from batch to batch. Sometimes, ironically enough, hothouse basil is sweeter than field basil. In very hot weather, basil grown outdoors can be bitter and metallic in flavor. Taste a leaf before you buy it. You don’t want to put up a big batch of pesto with inferior basil.
Place all the ingredients except the olive oil and cheese in a food processor or blender and process until combined. If you are adding cheese later, use just ½teaspoon salt and season to taste after the cheese is added. Add about half the oil and quickly puree, then add the remaining oil and process