Let the oil and egg be thoroughly chilled before beginning to make Mayonnaise. In summer it is well to stand the soup-plate in which the dressing is being mixed in a dish of cracked ice; stir constantly with a silver fork or a wooden spoon. Have the yolk entirely free from any white of the egg; add drop by drop the oil. The success depends on adding the oil slowly at first. It is well to spend half the time in incorporating the first two spoonfuls of oil; after that it can be added in larger quantities. After the dressing has become a little thick, alternate a few drops of lemon-juice or of vinegar with the oil; a little tarragon vinegar gives good flavor. If mustard is liked, add one quarter teaspoonful of dry mustard. Add the salt and pepper last. If the sauce curdles, take another yolk, and add slowly the curdled Mayonnaise. A few drops of ice water or a small bit of ice added to the mixture when it begins to curdle will sometimes bring it back.
This dressing will keep for some time in a closed jar in the ice-box. The proportions given are right, but it is usually desirable to make a larger quantity. With care more oil can be added to the egg, which will give more sauce.
A very safe mixture, and one recommended for summer, is made by using the yolk of a hard-boiled egg with a raw yolk. With this the dressing is more quickly made and seldom curdles. Lemon-juice makes a whiter dressing than vinegar, but it also makes it a little softer.