Whisk together all ingredients except the oil. You may also use a mixture of ½ lemon juice and ½ wine vinegar. Slowly incorporate the oil by droplets. If you're using a food processor, blend in the oil in a slow, steady stream.
This makes about ½ cup. If you choose to add fresh herbs, such as tarragon, basil, chives, or dill, stir in the herbs and correct seasoning just before dressing the salad.