Place two fresh egg yolks into an earthen bowl, with half a teaspoonful of ground English mustard, half a pinch of salt, half a saltspoonful of red pepper ; sharply stir with a wooden spoon for two or three minutes without ceasing. Pour in, drop by drop, one and a half cupfuls of the best olive oil. Should it become too thick, add, drop by drop, the equivalent of a teaspoonful of very good vinegar, stirring vigorously with the wooden spoon meanwhile. Taste, and if found a little too acid, gradually add a tablespoonful of oil, stirring continually until all added. The whole operation to prepare the above sauce will take from ten to twelve minutes. To avoid spoiling the sauce, the sweet oil should always be kept in a place of moderate temperature, say, from 700 to 750 Fahrenheit.