In a blender with a tamper or a food processor, add the herbs, salt, lemon juice, and miso paste. If you want a very smooth sauce, a blender is the way to go but if you want or don’t mind a bit of texture, the food processor will do the job.  Blend until fully broken down, then add the olive oil, with the machine running if possible. Keep blending for about 60-90 seconds to emulsify the oil.  Use right away or store in a tightly sealed jar in the refrigerator for up to 3 days.