Blend all ingredients except olive oil with a hand blender or in a food processor or blender. When mixture is smooth, begin adding oil, a few drops at a time, then a little more and faster. Watch the mixture as the oil goes in and if mixture becomes too thick before all oil is added, scrape sides and add a few drops of water to thin it down. Taste and adjust seasonings and oil to vinegar balance. Reserve in refrigerator until ready to use.