Put the egg, mustard, garlic, lemon juice, parley, and onion in a blender or food processor and process until smooth, about 15 seconds. With the processor running, pour the oil through the feed tube in a steady stream. Add the Worcestershire, season with salt, pepper, and hot sauce, and pulse to blend. Cover and let sit for 1 hour in the refrigerator before serving. Use within 24 hours.
*RAW EGG WARNING
The American Egg Board states: "There have been warnings against consuming raw or lightly cooked eggs on the grounds that the egg may be contaminated with Salmonella, a bacteria responsible for a type of foodborne illness. Healthy people need to remember that there is a very small risk and treat eggs and other raw animal foods accordingly. Use only properly refrigerated, clean, sound-shelled, fresh, grade AA or A eggs. Avoid mixing yolks and whites with the shell."
Yield: about 1 1/3 cups