Here is Julia's food processor mayonnaise, published later on. In my experience, it's foolproof.
Machine-Made Mayonnaise
From The Way to Cook by Julia Child
For 2-2½ cups
1 "large" egg
2 egg yolks
1 tsp. Dijon mustard
1/2 tsp. salt
2 tsp. freshly squeezed lemon juice and/or wine vinegar
1½ to 2 cups best-quality oil--peanut, olive, or other oil--all one or a mixture (see note below)
Freshly ground white pepper
Mosre mustard, salt, lemon juice and/or vinegar, as needed
Droplets of sour cream, sweet cream, or water--to lighten the finished sauce if it is too stiff
A food processor, fitted with the plastic blade, if possible (see note below)
Place the wholes egg, the yolks, and the teaspoon of mustard in the container of the processor; process 30 seconds with the plastic blade, 15 with the steel blade.
With the machine running, start adding the oil, pouring it in a thin stream of droplets--keep your eye on the stream to be sure it is going in very slowly. Keep the machine always running, and when you see that the sauce has thickened, you may add the oil a little faster. Stop the machine after 1½ cups or so of oil, and check on the sauce: it it seems very thick, add droplets of lemon or vinegar, and taste it for seasoning. (You do not need to use all of the oil; if you'd like a yellower sauce, for instance, 1½ cups may be sufficient.) Continue with the oil if you plan to use all of it.
Taste the sauce carefully for seasoning, briefly processing in more as necessary. If the sauce is too stiff or thick, process in droplets of cream or water.
Notes:
The oil to use: What is the mayonnaise to accompany? Cold lobster or crab, for instance, would want a light oil, neutral in taste, with perhaps just a dribble of olive oil for flavor. A salad strong with garlic and onions, on the other hand, will take, and even need, more pronounced tastes. For an all-purpose suace, as an example, use half to two-thirds peanut oil and the rest virgin olive oil.
Plastic vs. metal blade: The metal blade is so efficient that it often makes too stiff a sauce, and you'll want to thin it out. The shorter dull-edged plastic blade, however, which is a little slower in action gives a more tender result--if you can call a sauce tender!