This is the most delicious of all cold sauces. It is composed entirely of raw yolk of egg and oil, flavoured with a dash of vinegar. When made properly it should be of the consistency of butter in summer time. Many women cooks labour under the delusion that it requires the addition of cream. Mayonnaise sauce is made as follows:--Break an egg and separate the yolk from the white, and place the yolk at the bottom of a large basin. Next take a bottle of oil, which must be cool but bright; if the oil is cloudy, as it often is in cold weather, you cannot make the sauce. Nor can you if the oil has been kept in a warm place. Now proceed to let the oil drop, drop by drop, on the yolk of egg, and with a silver fork, or still better, a wooden one, beat the yolk of egg and oil quickly together. Continue to drop the oil, taking care that only a few drops drop at a time, especially at starting, and continue to beat the mixture lightly and quickly. Gradually the yolk of egg and oil will begin to get thick, first of all like custard. When this is the case a little more oil may be added at a time, but never more than a teaspoonful. As more oil is added, and the beating continues, the sauce gets thicker and thicker, till it is nearly as thick as butter in summer time. When it arrives at this stage no more oil should be added. A little tarragon vinegar may be added at the finish, or a little lemon juice. This makes the sauce whiter in colour. One yolk of egg will take a teacupful of oil. It is best to add pepper and salt when the salad is mixed. Mayonnaise sauce is by far the best sauce for lettuce salad. It will keep a day, but should be kept in a cool place, and the basin should be covered over with a moist cloth.
Source:
Cassell's Vegetarian Cookery
