Place egg, egg yolk, mustard, salt and pepper in a blender or food processor, and process until mixed.
With motor running, very slowly add oil in a thin steam, until mixture thickens.
Flavour with vinegar or lemon juice to taste.
Any one of these may also be stirred into a good bottled mayonnaise.
Aioli: Add 3-5 fat garlic cloves, crushed, to eggs at start.
Watercress: Add 190 ml watercress to egg mixture before adding oil (purée first if using bottled mayonnaise).
Pesto: Stir in 15-30 ml basil pesto or sun-dried tomato pesto into mayonnaise at the end.
Chilli (rouille): Add 1-2 ml crushed dried chilli, 2 cloves garlic, crushed, a dash of sugar and 5 ml tomato paste to eggs before blending. Add cayenne pepper or a drop or two of tabasco sauce for extra kick.
Thousand Island: Add tomato sauce, tomato paste, Worcestershire sauce and tabasco sauce, a little at a time, at the end.
Curry: Heat 10 ml good-quality hot curry powder and 2 ml each ground cumin and coriander in a pan until aromatic. Add a few teaspoonfuls of chutney and a little fresh orange juice. Mix, cool and add at the end.
Tapenade: Add chopped black olives, anchovies, garlic and capers at the end.
Tartare: Add capers, parsley and gherkins at the end.
Blue cheese: Stir in grated blue cheese at the end.
Low fat: Use half and half mayonnaise and natural yoghurt. Any of the options given here can also be added.
Makes 375 ml