Mayonnaise is very easy to make if you follow a few rules. First, have all the ingredients at room temperature before you begin. Add the oil very slowly, drop by drop, at the beginning until the sauce begins to emulsify; then you may add the remainder in a steady stream without risk of breaking the emulsion. If the sauce does separate, whisk in 5 ml (1 tsp) cold water. If the mayonnaise remains broken, whisk 5 ml (1 tsp) of the broken mayonnaise into 5 ml (1 tsp) mustard in a warm, dry bowl until creamy (mustard helps to emulsify the sauce). Then gradually whisk in the remaining mayonnaise.
A simpic mayonnaise is the foundation for a number of sauces. With the addition of puriéed herbs and green leaves it becomes a Sauce Verte, flavoured with puréed red pepper it becomes a Sauce Rouille, and with chopped capers, onions, gherkins, and hard-boiled eggs it becomes a spicy Sauce Tartare.