Put all ingredients in a jar just wider than the head of the immersion blender. The oil is gradually emulsified into the other ingredients. When using a food processor or a blender, add all ingredients except the oil, and gradually add in the oil with the other ingredients. However, I find that this recipe works best with an immersion blender. The immersion blender creates a vortex gradually pulling the oil down into the blades to emulsify the oil into the other ingredients.
Do not pulse or move the head of the immersion blender. As mayonnaise forms, slowly tilt and lift the head of the immersion blender until all oil is emulsified.
Season with salt to taste.
Store in a sealed container in the refrigerator for up to two weeks.