From "Mastering the Art of French Cooking". JULIA'S POINTS TO REMEMBER : Temperature: Mayonnaise is easiest to make when all ingredients are at normal room temperature. Warm the mixing bowl in hot water to take the chill off the egg yolks. Heat the oil to tepid if it is cold. Egg Yolks: Always beat the egg yolks for a minute or two before adding anything to them. As soon as they are thick and sticky, they are ready to absorb the oil. Adding the Oil: The oil must be added very slowly at first, in droplets, until the emulsion process begins and the sauce thickens into a heavy cream. After this, the oil may be incorporated more rapidly. Proportions: The maximum amount of oil one U.S. Large egg yolk will absorb is 6 ounces or 3/4 cup. When this maximum is exceeded, the binding properties of the egg yolks break down, and the sauce thins out or curdles. If you have never made made mayonnaise before, it is safest not to exceed 1/2 cup of oil per egg yolk. REMEDY FOR TURNED MAYONNAISE: You will never have trouble with freshly made mayonnaise if you have beaten the egg yolks thoroughly in a warmed bowl before adding the oil, if the oil has been added in droplets until the sauce has commenced to thicken, and if you have not exceeded the maximum proportions of 3/4 cup of oil per egg yolk. A mayonnaise has turned when it refuses to thicken, or, in a finished mayonnaise, when the oil releases itself from suspension and the sauce curdles. In either case, the remedy is simple. Warm a mixing bowl in hot water. Dry it. Add 1 teaspoon of prepared mustard and 1 teaspoon of sauce. Beat with a wire whip for several seconds unil they cream and thicken together. Beat in the rest of the sauce by teaspoons, thickening each addition before adding the next. This always works. Just be sure you add the turned sauce a little bit at a time, particularly at first. REFRIGERATION: After several days under refrigeration, mayonnaise has a tendency to thin out, especially if it is stirred before it comes to room temperature. If it does turn, bring it back using the preceding system.