Mayonnaise Sauce
Put one yolk of egg (quite free from any white), half a teaspoonful of salt, and a pinch of cayenne, into a bowl standing in ice. Stir constantly, and add one cupful of pure olive oil, drop by drop. The goodness of the sauce depends upon adding the oil slowly. When it begins to get thick, alternate a few drops of tarragon vinegar with the oil till you have put in one and a half teaspoonfuls of vinegar (lemon juice may be used instead). In summer it is a good plan to mix the yolk of a hard-boiled egg with the raw one; the sauce is made more quickly and is less likely to curdle.