Parsley has a pronounced flavor of its own that is fully released during blending. If you want a milder pesto, mix flat-leaf parsley and basil in a 2:1 ratio – this is a culinarily sound combination and not a compromise.
Bitter trap: Working in stages matters for parsley pesto too. First coarsely pre-chop the parsley, pine nuts, Parmesan, and garlic on setting 5 to 6 for about 10 to 15 seconds, then stop the blender. Restart on setting 1 and let the olive oil run in slowly through the lid opening. As soon as the pesto is uniform, stop right away. You can also stir in the last third of the oil with a spoon – this is the surest way to avoid any bitterness.
Preparation: Use only the flat leaves and tender stems. The coarse lower stems make the pesto fibrous and can be used together with the cooking liquid for broths. Wash the parsley well and pat it really dry – water residue thins the pesto and shortens its shelf life.