Place into a small bowl the mustard, egg yolk and only half amount of the lemon juice. With a fork whisk the ingredients together. (Yes you can whisk with a fork too!)
Continue to whisk with your wrist non stop and start pouring in a constant amount of oil. The egg, mustard and oil will form an emulsion, so the sauce will get thicker while continuously pouring in the oil. Keep on whisking until you have added all the oil. The sauce should be thick now as seen in the picture.
Add the black pepper and remaining lemon juice to the sauce and whisk the sauce again.
At this point you can also add chopped chives or other ingredients to make another sauce such as sauce tartar. We usually serve mayonnaise with boiled vegetables such as carrot and potato and boiled fish (exp. trout) Fresh homemade mayo should be consumed the same day.