Place everything except the oil in a blender or food processor. Process until very smooth.
Keep the machine running as you drizzle in the oil.
When all the oil is incorporated, turn off the machine.
Transfer to a container, cover and refrigerate.
Green Mayo: Add a handful each of chopped parsley and chives to step one.
Sesame Mayo: Substitute a few tablespoon of the oil with sesame oil.
From The Moosewood Cookbook, by Mollie Katzen.