Combine the egg yolks, whole egg, mustard, salt, pepper and vinegar. With the motor running, drizzle in the oil through the funnel, in a slow, steady stream. You will see it getting thicker and thicker the more oil you add. Once it is all blended, taste to see if you want to add more salt or pepper or a drop more vinegar.
Use a spatula to scrape the mayonnaise into a container.
Cover and refrigerate.